Display Device and Electronic Device

ABSTRACT

To improve color reproduction areas in a display device having light-emitting elements. A display region has a plurality of picture elements. Each picture element includes: first and second pixels each including a light-emitting element which has a chromaticity whose x-coordinate in a CIE-XY chromaticity diagram is 0.50 or more; third and fourth pixels each including a light-emitting element which has a chromaticity whose y-coordinate in the diagram is 0.55 or more; and fifth and sixth pixels each including a light-emitting element which has a chromaticity whose x-coordinate and y-coordinate in the diagram are 0.20 or less and 0.25 or less, respectively. The light-emitting elements in the first and second pixels have different emission spectrums from each other; the light-emitting elements in the third and fourth pixels have different emission spectrums from each other; and the light-emitting elements in the fifth and sixth pixels have different emission spectrums from each other.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a display device equipped with alight-emitting element or, an electro-optical element in a pixel. Inparticular, the present invention relates to a display device having alayer including an organic material, a fluorescent material, or aphosphorescent material in the light-emitting element.

2. Description of the Related Art

A display device having a light-emitting element which includes a layerof an organic material between a pair of electrodes and emits light whena current is supplied between the electrodes has been developed. Such adisplay device has an advantage in reducing thickness and weight, hashigh visibility due to the self-luminance, and has high response speed.In addition, since power consumption of such a display device maypotentially be made very small, it has been actively developed as adevice of next generation, and some of such devices have been put intopractical use.

In the display device using the light-emitting element having theaforementioned configuration, high image quality and widening of a colorgamut have been expected. For example, a display device which canreproduce and display accurate colors in editing in a printingoperation, seeing and listening to a work of art, movies, or the like,and catching a real color exactly in telemedicine, has been stronglyexpected. In view of this, in order to improve a color gamut which canbe viewed by human eyes, research to optimize a structure such asimprovement of color purity and widening of a color gamut has beencarried out (for example, see Reference 1: Published Japanesetranslation of PCT International Publication for Patent Application No.2001-039554).

However, there is still a surplus in a color gamut which can be viewedby human eyes, and thus, a color reproduction area of a display deviceso far is still insufficient. FIG. 39 shows the CIE-XY chromaticitydiagram which is established by COMMISSION INTERNATIONALE DE L'ECLAIRAGE(INTERNATIONAL COMMISSION ON ILLUMINATION: CIE) managing standards ofcolor internationally. In an outer boundary of the diagram, a pointwhich is near the rightmost end corresponds to an emission spectrum of700 nm of red monochromatic light; a point which is near the uppermostend corresponds to an emission spectrum of 546.1 nm of greenmonochromatic light; and a point which is near the lowermost endcorresponds to an emission spectrum of 435.8 nm of blue monochromaticlight. In this chromaticity diagram, brightness (chroma) is lower in theinner side since the outer boundary of the graph (a visible area)corresponds to an emission spectrum of monochromatic light while theinner side thereof corresponds to a combination color obtained bycombining different kinds of monochromatic light. In the case ofexpressing a color by an additive color mixture, a plurality of standardcolors can reproduce only a color which lies in a position surroundedwith a polygon formed of points which are shown in the CIE-XYchromaticity diagram.

When red (R) is shown by the CIE-XY chromaticity diagram, human eyes canperceive a color which has a coordinate near a right region of thechromaticity diagram (a region surrounded with the circumference of thechromaticity diagram and a dotted line 3901 in FIG. 39) as red. Inaddition, when green (G) is shown by the CIE-XY chromaticity diagram,human eyes can perceive a color which has a coordinate near an upperregion of the chromaticity diagram (a region surrounded with thecircumference of the chromaticity diagram and a dotted line 3902 in FIG.39) as green. When blue (B) is shown by the CIE-XY chromaticity diagram,human eyes can perceive a color which has a coordinate near a lowerregion of the chromaticity diagram (a region surrounded with thecircumference of the chromaticity diagram and dotted lines 3903 and 3904in FIG. 39) as blue. As a specific example, a hi-vision (high definitiontelevision broadcasting; HDTV) standard can be given, which haschromaticity coordinates of R (x=0.67, y=0.33), G (x=0.21, y=0.71), andB (x=0.14, y=0.08) (a triangle 3905 in FIG. 39).

According to the method disclosed in Reference 1, a color reproductionarea can be expanded in directions of arrows in FIG. 39 by increasingcolor purity, and brightness of colors recognized by human eyes can beincreased. However, there is still a surplus in a color gamut which canbe viewed by human eyes. Therefore, it is an essential task to expandthe color reproduction area by satisfying the surplus in the color gamutwhich can be viewed by human eyes.

SUMMARY OF THE INVENTION

In view of this, it is an object of the invention to accomplish theaforementioned task in a display device equipped with a light-emittingelement, so that the color reproduction area can be improved and thecolor gamut which can be viewed by human eyes can be widened.

A display device in accordance with one aspect of the invention includesa display region having a plurality of picture elements. Each pictureelement includes: a first pixel and a second pixel each including alight-emitting element, the light-emitting element having a chromaticitywhose x-coordinate in a CIE-XY chromaticity diagram is 0.50 or more; athird pixel and a fourth pixel each including a light-emitting element,the light-emitting element having a chromaticity whose y-coordinate inthe CIE-XY chromaticity diagram is 0.55 or more; and a fifth pixel and asixth pixel each including a light-emitting element, the light-emittingelement having a chromaticity whose x-coordinate and y-coordinate in theCIE-XY chromaticity diagram are 0.20 or less and 0.25 or less,respectively. The light-emitting elements provided in the first pixeland the second pixel have different emission spectrums from each other;the light-emitting elements provided in the third pixel and the fourthpixel have different emission spectrums from each other, and thelight-emitting elements provided in the fifth pixel and the sixth pixelhave different emission spectrums from each other.

A display device in accordance with one aspect of the invention includesa display region having a plurality of picture elements. Each pictureelement includes: a first pixel and a second pixel each including alight-emitting element, the light-emitting element having a chromaticitywhose x-coordinate in a CIE-XY chromaticity diagram is 0.50 or more; athird pixel and a fourth pixel each including a light-emitting element,the light-emitting element having a chromaticity whose y-coordinate inthe CIE-XY chromaticity diagram is 0.55 or more; and a fifth pixel and asixth pixel each including a light-emitting element, the light-emittingelement having a chromaticity whose x-coordinate and y-coordinate in theCIE-XY chromaticity diagram are 0.20 or less and 025 or less,respectively. The light-emitting elements provided in the first pixeland the second pixel emit light with colors of different coordinatesfrom each other in the CIE-XY chromaticity diagram; the light-emittingelements provided in the third pixel and the fourth pixel emit lightwith colors of different coordinates from each other in the CIE-XYchromaticity diagram; and the light-emitting elements provided in thefifth pixel and the sixth pixel emit light with colors of differentcoordinates from each other in the CIE-XY chromaticity diagram.

A display device in accordance with one aspect of the invention includesa display region having a plurality of picture elements. Each pictureelement includes: a first pixel and a second pixel each including alight-emitting element, the light-emitting element having a chromaticitywhose x-coordinate in a CIE-XY chromaticity diagram is 0.50 or more; athird pixel and a fourth pixel each including a light-emitting element,the light-emitting element having a chromaticity whose y-coordinate inthe CIE-XY chromaticity diagram is 0.55 or more; and a fifth pixel and asixth pixel each including a light-emitting element, the light-emittingelement having a chromaticity whose x-coordinate and y-coordinate in theCIE-XY chromaticity diagram are 0.20 or less and 0.25 or less,respectively. The light-emitting elements provided in the first pixeland the second pixel are formed of different materials from each otherto have different emission spectrums; the light-emitting elementsprovided in the third pixel and the fourth pixel are formed of differentmaterials from each other to have different emission spectrums; and thelight-emitting elements provided in the fifth pixel and the sixth pixelare formed of different materials from each other to have differentemission spectrums.

A display device in accordance with one aspect of the invention includesa display region having a plurality of picture elements. Each pictureelement includes: a first pixel and a second pixel each including alight-emitting element, the light-emitting element having a chromaticitywhose x-coordinate in a CIE-XY chromaticity diagram is 0.50 or more; athird pixel and a fourth pixel each including a light-emitting element,the light-emitting element having a chromaticity whose y-coordinate inthe CIE-XY chromaticity diagram is 0.55 or more; and a fifth pixel and asixth pixel each including a light-emitting element, the light-emittingelement having a chromaticity whose x-coordinate and y-coordinate in theCIE-XY chromaticity diagram are 0.20 or less and 0.25 or less,respectively. The light-emitting elements provided in the first pixeland the second pixel are formed to have different thickness from eachother to have different emission spectrums; the light-emitting elementsprovided in the third pixel and the fourth pixel are formed to havedifferent thickness from each other to have different emissionspectrums; and the light-emitting elements provided in the fifth pixeland the sixth pixel are formed to have different thickness from eachother to have different emission spectrums.

A display device in accordance with one aspect of the invention includesa display region having a plurality of picture elements. Each pictureelement includes: a first pixel and a second pixel each including alight-emitting element, the light-emitting element having a chromaticitywhose x-coordinate in a CIE-XY chromaticity diagram is 0.50 or more; athird pixel and a fourth pixel each including a light-emitting element,the light-emitting element having a chromaticity whose y-coordinate inthe CIE-XY chromaticity diagram is 0.55 or more; and a fifth pixel and asixth pixel each including a light-emitting element, the light-emittingelement having a chromaticity whose x-coordinate and y-coordinate in theCIE-XY chromaticity diagram are 0.20 or less and 0.25 or less,respectively. The first pixel and the second pixel have color filterswith different transmission properties from each other, thereby lightwhich has traveled through each of the color filters has a differentemission spectrum from each other; the third pixel and the fourth pixelhave color filters with different transmission properties from eachother, thereby light which has traveled through each of the colorfilters has a different emission spectrum from each other; and the fifthpixel and the sixth pixel have color filters with different transmissionproperties from each other, thereby light which has traveled througheach of the color filters has a different emission spectrum from eachother.

A display device in accordance with one aspect of the invention includesa display region having a plurality of picture elements. Each pictureelement includes: a first pixel and a second pixel each including alight-emitting element, the light-emitting element having a chromaticitywhose x-coordinate in a CIE-XY chromaticity diagram is 0.50 or more; athird pixel and a fourth pixel each including a light-emitting element,the light-emitting element having a chromaticity whose y-coordinate inthe CIE-XY chromaticity diagram is 0.55 or more; and a fifth pixel and asixth pixel each including a light-emitting element, the light-emittingelement having a chromaticity whose x-coordinate and y-coordinate theCIE-XY chromaticity diagram are 0.20 or less and 0.25 or less,respectively. The light-emitting elements provided in the first pixeland the second pixel are formed of different materials from each other,and emit light with colors of different coordinates in the CIE-XYchromaticity diagram; the light-emitting elements provided in the thirdpixel and the fourth pixel are formed of different materials from eachother, and emit light with colors of different coordinates in the CIE-XYchromaticity diagram; and the light-emitting elements provided in thefifth pixel and the sixth pixel are formed of different materials fromeach other, and emit light with colors of different coordinates in theCIE-XY chromaticity diagram.

A display device in accordance with one aspect of the invention includesa display region having a plurality of picture elements. Each pictureelement includes: a first pixel and a second pixel each including alight-emitting element, the light-emitting element having a chromaticitywhose x-coordinate in a CIE-XY chromaticity diagram is 0.50 or more; athird pixel and a fourth pixel each including a light-emitting element,the light-emitting element having a chromaticity whose y-coordinate inthe CIE-XY chromaticity diagram is 0.55 or more; and a fifth pixel and asixth pixel each including a light-emitting element, the light-emittingelement having a chromaticity whose x-coordinate and y-coordinate in theCIE-XY chromaticity diagram are 0.20 or less and 0.25 or less,respectively. The light-emitting elements provided in the first pixeland the second pixel are formed to have different thickness from eachother, and emit light with colors of different coordinates in the CIE-XYchromaticity diagram; the light-emitting elements provided in the thirdpixel and the fourth pixel are formed to have different thickness fromeach other, and emit light with colors of different coordinates in theCIE-XY chromaticity diagram; and the light-emitting elements provided inthe fifth pixel and the sixth pixel are formed to have differentthickness from each other, and emit light with colors of differentcoordinates in the CIE-XY chromaticity diagram.

A display device in accordance with one aspect of the invention includesa display region having a plurality of picture elements. Each pictureelement includes: a first pixel and a second pixel each including alight-emitting element, the light-emitting element having a chromaticitywhose x-coordinate in a CIE-XY chromaticity diagram is 0.50 or more; athird pixel and a fourth pixel each including a light-emitting element,the light-emitting element having a chromaticity whose y-coordinate inthe CIE-XY chromaticity diagram is 0.55 or more; and a fifth pixel and asixth pixel each including a light-emitting element, the light-emittingelement having a chromaticity whose x-coordinate and y-coordinate in theCIE-XY chromaticity diagram are 0.20 or less and 0.25 or less,respectively. The first pixel and the second pixel have color filterswith different transmission properties from each other, and light thathas traveled through one of the color filters has a color of a differentcoordinate from light that has traveled through the other color filterin the CIE-XY chromaticity diagram; the third pixel and the fourth pixelhave color filters with different transmission properties from eachother, and light that has traveled through one of the color filters hasa color of a different coordinate from light that has traveled throughthe other color filter in the CIE-XY chromaticity diagram; and the fifthpixel and the sixth pixel have color filters with different transmissionproperties from each other, and light that has traveled through one ofthe color filters has a color of a different coordinate from light thathas traveled through the other color filter in the CIE-XY chromaticitydiagram.

Either one of the light-emitting element provided in the first pixel orthe light-emitting element provided in the second pixel may have achromaticity whose x-coordinate and y-coordinate in the CIE-XYchromaticity diagram are 0.6 or more and 0.35 or less, respectively;either one of the light-emitting element provided in the third pixel orthe light-emitting element provided in the fourth pixel may have achromaticity whose x-coordinate and y-coordinate in the CIE-XYchromaticity diagram are 0.3 or less and 0.6 or more, respectively; andeither one of the light-emitting element provided in the fifth pixel orthe light-emitting element provided in the sixth pixel may have achromaticity whose x-coordinate and y-coordinate in the CIE-XYchromaticity diagram are 0.15 or less and 0.2 or less, respectively.

The picture element may include a light-emitting element which emitswhite light.

The first pixel and the second pixel may have light-emitting regionswith different area dimensions from each other; the third pixel and thefourth pixel may have light-emitting regions with different areadimensions from each other; and the fifth pixel and the sixth pixel mayhave light-emitting regions with different area dimensions from eachother.

The light-emitting element may be an electroluminescent (EL: ElectroLuminescence) element (e.g., an organic EL element, an inorganic ELelement, or an EL element containing organic and inorganic materials).

Note that a region in the CIE-XY chromaticity diagram in thisspecification corresponds to a region showing visible light in theCIE-XY chromaticity diagram which can be recognized by human eyes.

Note also that a switch described in this specification can employvarious types of elements. An electrical switch, a mechanical switch, orthe like is given as an example. That is, anything that can control acurrent flow can be employed, and thus, various types of elements can beemployed without limiting to a certain element. For example, it may be atransistor, a diode (e.g., a PN junction diode, a PIN diode, a Schottkydiode, or a diode-connected transistor), a thyristor, or a logic circuitcombining such elements. Therefore, in the case of employing atransistor as a switch, the polarity (the conductivity type) of thetransistor is not particularly limited to a certain type since itoperates just as a switch. However, when off-current is preferred to besmall, a transistor of a polarity with small off-current is desirablyemployed. As a transistor with small off-current, there is a transistorprovided with an LDD region, a transistor with a multi-gate structure,or the like. In addition, it is desirable that an n-channel transistorbe employed when a potential of a source terminal of the transistorbeing operated as a switch is closer to the low-potential-side powersupply (e.g., Vss, GND, or 0 V), while a p-channel transistor beemployed when the potential of the source terminal is closer to thehigh-potential-side power supply (e.g., Vdd). This helps the switchoperate efficiently since the absolute value of the gate-source voltageof the transistor can be increased.

A CMOS switch may also be employed by using both n-channel and p-channeltransistors. By employing a CMOS switch, the switch can efficientlyoperate as a switch since current can flow when either one of thep-channel transistor or the n-channel transistor is turned on. Forexample, voltage can be appropriately output regardless of whethervoltage of an input signal of the switch is high or low. Further, sincea voltage amplitude value of a signal for turning on or off the switchcan be suppressed, power consumption can be reduced.

When a transistor is employed as a switch, the switch includes an inputterminal (one of either a source terminal or a drain terminal), anoutput terminal (the other of either the source terminal or the drainterminal), and a terminal for controlling electrical conduction (a gateterminal). On the other hand, when a diode is employed as a switch, theswitch may not have a terminal for controlling electrical conduction.Therefore, the number of wires for controlling terminals can be reduced.

Note that in this specification, the description “being connected”includes a case where elements are electrically connected, a case whereelements are functionally connected, and a case where elements aredirectly connected. Accordingly, in the configurations disclosed in thisspecification, other elements may be sandwiched between elements havinga predetermined connecting relation. For example, one or more elementswhich enable an electrical connection (e.g., a switch, a transistor, acapacitor t, an inductor, a resistor, or a diode) may be provided. Inaddition, one or more circuits which enable a functional connection maybe provided in addition to the predetermined elements, such as a logiccircuit (e.g., an inverter, a NAND circuit, or a NOR circuit), a signalconverter circuit (e.g., a DA converter circuit, an AD convertercircuit, or a gamma correction circuit), a potential level convertercircuit (e.g., a power supply circuit such as a boosting circuit or avoltage lower control circuit, or a level shifter circuit for changing apotential level of an H signal or an L signal), a voltage source, acurrent source, a switching circuit, or an amplifier circuit (e.g., acircuit which can increase the signal amplitude, the amount of current,or the like, such as an operational amplifier, a differential amplifiercircuit, a source follower circuit, or a buffer circuit), a signalgenerating circuit, a memory circuit, or a control circuit.Alternatively, the elements may be directly connected withoutinterposing other elements or other circuits therebetween.

When it is obvious that elements are connected without interposing otherelements or circuits therebetween, such elements are described as “beingdirectly connected” in this specification. On the other hand, whenelements are described as “being electrically connected”, the followingcases can be considered: a case where such elements are electricallyconnected (that is, connected by interposing other elementstherebetween), a case where such elements are functionally connected(that is, connected by interposing other circuits therebetween), and acase where such elements are directly connected (that is, connectedwithout interposing other elements or other circuits therebetween).

Note that in this specification, various types of transistors can beapplied to a transistor. Therefore, types of transistors which can beapplied are not limited to a certain type. For example, a thin filmtransistor (TFT) including a non-single crystalline semiconductor filmtypified by amorphous silicon or polycrystalline silicon can be applied.Accordingly, various advantages can be provided that such transistorscan be manufactured at a low manufacturing temperature, can bemanufactured at low cost, can be formed over a large substrate as wellas a light-transmissive substrate, and further, such transistors cantransmit light. In addition, the transistors can be formed by using asemiconductor substrate, an SOI substrate, or the like. In addition, aMOS transistor, a junction transistor, a bipolar transistor, or the likecan be employed. Accordingly, transistors with few variations,transistors with a high current supply capacity, and transistors with asmall size can be manufactured, and thereby a circuit with low powerconsumption can be constructed by using such transistors. Further, atransistor including a compound semiconductor such as ZnO, a-InGaZnO,SiGe, or GaAs, or a thin film transistor obtained by thinning suchcompound semiconductors can be employed. Accordingly, such transistorscan be manufactured at a low manufacturing temperature, can bemanufactured at a room temperature, and can be formed directly over alow heat-resistant substrate such as a plastic substrate or a filmsubstrate. A transistor or the like formed by ink-jet method or aprinting method may also be employed. Accordingly, such transistors canbe manufactured at a room temperature, can be manufactured at a lowvacuum, and can be manufactured over a large substrate. In addition,since such transistors can be manufactured without using a mask(reticle), the layout of the transistors can be easily changed. Atransistor including an organic semiconductor or a carbon nanotube, orother transistors can be applied as well. Accordingly, the transistorscan be formed over a substrate which can be bent. Note that a non-singlecrystalline semiconductor film may include hydrogen or halogen. Inaddition, various types of substrates can be applied to a substrate overwhich transistors are formed without limiting to a certain type.Accordingly, transistors may be formed over, for example, a singlecrystalline substrate, an SOI substrate, a glass substrate, a quartzsubstrate, a plastic substrate, a paper substrate, a cellophanesubstrate, a stone substrate, a stainless steel substrate, a substratemade of a stainless steel foil, or the like. In addition, after formingtransistors over a substrate, the transistors may be transposed ontoanother substrate. As for another substrate, a single crystallinesubstrate, an SOI substrate, a glass substrate, a quartz substrate, aplastic substrate, a paper substrate, a cellophane substrate, a stonesubstrate, a stainless steel substrate, a substrate made of a stainlesssteel foil, or the like may be employed. By using the aforementionedsubstrates, transistors with excellent properties and with low powerconsumption can be formed, and thus, a device with high durability andhigh heat resistance can be formed.

The structure of a transistor may be various modes. Therefore, thestructure of the transistor is not limited to a certain type. Forexample, a multi-gate structure having two or more gate electrodes maybe used. When a multi-gate structure is employed, a structure wherechannel regions are connected in series is provided; therefore, astructure where a plurality of transistors are connected in series isprovided. By employing a multi-gate structure, off-current can bereduced as well as the withstand voltage can be increased to improve thereliability of the transistor, and even if a drain-source voltagefluctuates when the transistor operates in the saturation region, flatcharacteristics can be provided without causing fluctuations ofdrain-source current very much. In addition, a structure where gateelectrodes are formed above and below a channel may be employed. Byusing a structure where gate electrodes are formed above and below achannel, the channel region is enlarged to increase the amount ofcurrent flowing therethrough, and a depletion layer can be easily formedto improve the S value. When gate electrodes are formed above and belowa channel, a structure where a plurality of transistors are connected inparallel is provided.

In addition, any of the following structures may be employed: astructure where a gate electrode is formed above a channel; a structurewhere a gate electrode is formed below a channel; a staggered structure;an inversely staggered structure; and a structure where a channel regionis divided into a plurality of regions, and the divided regions areconnected in parallel or in series. In addition, a channel (or a part ofit) may overlap with a source electrode or a drain electrode. By forminga structure where a channel (or a part of it) overlaps with a sourceelectrode or a drain electrode, electric charges can be prevented fromgathering locally in a part of the channel, which would otherwise causean unstable operation. In addition, an LDD (Lightly Doped Drain) regionmay be provided. By providing an LDD region, off-current can be reducedas well as the withstand voltage can be increased to improve thereliability of the transistor, and even if a drain-source voltagefluctuates when the transistor operates in the saturation region, flatcharacteristics can be provided without causing fluctuations of adrain-source current very much.

Note that various types of transistors may be employed in thisspecification, and such transistors can be formed over various types ofsubstrates. Accordingly, all of the circuits may be formed over a glasssubstrate, a plastic substrate, a single crystalline substrate, an SOIsubstrate, or any other substrates. By forming all of the circuits overthe same substrate, the number of component parts can be reduced to cutcost, as well as the number of connections to the circuit components canbe reduced to improve the reliability. Alternatively, parts of thecircuits may be formed over one substrate while the other parts of thecircuits may be formed over another substrate. That is, not all of thecircuits are required to be formed over the same substrate. For example,parts of the circuits may be formed with transistors over a glasssubstrate while the other parts of the circuits may be formed over asingle crystalline substrate, so that the IC chip is connected to theglass substrate by COG (Chip On Glass). Alternatively, the IC chip maybe connected to the glass substrate by TAB (Tape Automated Bonding) or aprinted wiring board. In this manner, by forming parts of the circuitsover the same substrate, the number of component parts can be reduced tocut cost, as well as the number of connections to the circuit componentscan be reduced to improve the reliability. In addition, by forming aportion with a high driving voltage or a portion with high drivingfrequency which would consume large power over another substrate,increase of power consumption can be prevented.

Note that a transistor is an element having at least three terminals ofa gate, a drain, and a source. The transistor has a channel regionbetween a drain region and a source region, and can supply a currentthrough the drain region, the channel region, and the source region.Here, since the source and the drain of the transistor may changedepending on the structure, the operating conditions, and the like ofthe transistor, it is difficult to define which is a source or a drain.Therefore, in the invention, a region functioning as a source and adrain may not be called the source or the drain. In such a case, forexample, one of the source and the drain may be called a first terminaland the other terminal may be called a second terminal.

Note also that a transistor may be an element having at least threeterminals of a base, an emitter, and a collector. In this case also, oneof the emitter and the collector may be similarly called a firstterminal and the other terminal may be called a second terminal.

A gate means all of or a part of a gate electrode and a gate wire (alsocalled a gate line, a gate signal line, or the like). A gate electrodemeans a conductive film which overlaps with a semiconductor forming achannel region, an LDD region, or the like with a gate insulating filmsandwiched therebetween. A gate wire means a wire for connecting eachgate electrode of each pixel, or a wire for connecting a gate electrodeto another wire.

However, there is a portion functioning as both a gate electrode and agate wire. Such a region may be called either a gate electrode or a gatewire. That is, there is a region where a gate electrode and a gate wirecannot be clearly distinguished from each other. For example, in thecase where a channel region overlaps with an extended gate wire, theoverlapped region functions as both a gate wire and a gate electrode.Accordingly, such a region may be called either a gate electrode or agate wire.

In addition, a region formed of the same material as a gate electrodeand connected to the gate electrode may also be called a gate electrode.Similarly, a region formed of the same material as a gate wire andconnected to the gate wire may also be called a gate wire. In a strictsense, such a region may not overlap with a channel region, or may nothave a function of connecting to another gate electrode. However, thereis a region formed of the same material as a gate electrode or a gatewire and connected to the gate electrode or the gate wire in order tosatisfy a sufficient manufacturing margin. Accordingly, such a regionmay also be called either a gate electrode or a gate wire.

In a multi-gate transistor, for example, a gate electrode of onetransistor is often connected to a gate electrode of another transistorby using a conductive film which is formed of the same material as thegate electrode. Since such a region is a region for connecting a gateelectrode to another gate electrode, it may be called a gate wire, whileit may also be called a gate electrode since a multi-gate transistor canbe considered as one transistor. That is, a region which is formed ofthe same material as a gate electrode or a gate wire and connectedthereto may be called either the gate electrode or the gate wire.

In addition, for example, a part of a conductive film which connects agate electrode and a gate wire may also be called either a gateelectrode or a gate wire.

Note that a gate terminal means a part of a gate electrode or a part ofa region which is electrically connected to the gate electrode.

Note also that a source means all of or a part of a source region, asource electrode, and a source wire (also called a source line, a sourcesignal line, or the like). A source region means a semiconductor regioncontaining a large amount of p-type impurities (e.g., boron or gallium)or n-type impurities (e.g., phosphorus or arsenic). Accordingly, aregion containing a slight amount of p-type impurities or n-typeimpurities, namely, an LDD (Lightly Doped Drain) region is not includedin the source region. A source electrode is a part of a conductive layerformed of a different material from a source region, and electricallyconnected to the source region. However, there is a case where a sourceelectrode and a source region are collectively called a sourceelectrode. A source wire is a wire for connecting each source electrodeof each pixel, or a wire for connecting a source electrode to anotherwire.

However, there is a portion functioning as both a source electrode and asource wire. Such a region may be called either a source electrode or asource wire. That is, there is a region where a source electrode and asource wire cannot be clearly distinguished from each other. Forexample, in the case where a source region overlaps with an extendedsource wire, the overlapped region functions as both a source wire and asource electrode. Accordingly, such a region may be called either asource electrode or a source wire.

In addition, a region formed of the same material as a source electrodeand connected to the source electrode, or a portion for connecting asource electrode to another source electrode may be called a sourceelectrode. A part of a source wire which overlaps with a source regionmay also be called a source electrode. Similarly, a region formed of thesame material as a source wire and connected to the source wire may becalled a source wire. In a strict sense, such a region may not have afunction of connecting to another source electrode. However, there is aregion formed of the same material as a source electrode or a sourcewire, and connected to the source electrode or the source wire in orderto satisfy a sufficient manufacturing margin. Accordingly, such a regionmay also be called either a source electrode or a source wire.

In addition, for example, a part of a conductive film which connects asource electrode and a source wire may be called either a sourceelectrode or a source wire.

Note that a source terminal means a part of a source region, a part of asource electrode, or a part of a region electrically connected to thesource electrode.

Note also that the same can be said for a drain.

In this specification, a semiconductor device means a device having acircuit including semiconductor elements (e.g., transistors or diodes).The semiconductor device may also include all devices that can functionby utilizing semiconductor characteristics.

In addition, a display device means a device having display elements(e.g., liquid crystal elements or light-emitting elements). Note thatthe display device may also include a display panel itself where aplurality of pixels including display elements such as liquid crystalelements or EL elements are formed over the same substrate as aperipheral driver circuit for driving the pixels. In addition, thedisplay device may include a peripheral driver circuit disposed over thesubstrate by wire bonding or bump bonding, namely, chip-on-glass (COG).Further, the display device may include a flexible printed circuit (FPC)or a printed wiring board (PWB) attached to the display panel (e.g., anIC, a resistor, a capacitor, an inductor, or a transistor). Such adisplay device may also include an optical sheet such as a polarizingplate or a retardation plate. Further, the display device may include abacklight unit (which may include a light conducting plate, a prismsheet, a diffusion sheet, a reflective sheet, and a light source (e.g.,an LED or a cold cathode tube)). In addition, a light-emitting devicemeans a display device having self-luminous display elements,particularly, such as EL elements or elements used for an FED. A liquidcrystal display device means a display device having liquid crystalelements.

A display element, a display device, a light-emitting element, and alight-emitting device may include various types of modes and variouselements. For example, as the display element, the display device, thelight-emitting element, and the light-emitting device, there is adisplay medium whose contrast changes by an electromagnetic action, suchas an EL element (e.g., an organic EL element, an inorganic EL element,or an EL element containing both organic and inorganic materials); anelectron-emissive element; a liquid crystal element; electronic ink; agrating light valve (GLV); a plasma display (PDP); a digital micromirrordevice (DMD); a piezoelectric ceramic element; or a carbon nanotube. Inaddition, a display device using an EL element includes an EL display; adisplay device using an electron-emissive element includes a fieldemission display (FED), an SED-type flat panel display (SED:Surface-conduction Electron-emitter Display), or the like; a displaydevice using a liquid crystal element includes a liquid crystal display,a transmissive liquid crystal display, a semi-transmissive liquidcrystal display, and a reflective liquid crystal display; and a displaydevice using electronic ink includes electronic paper.

In this specification, an expression that an object is “formed on” or“formed above” another object does not necessarily mean that the objectis in direct contact with another object. The expression may include acase where two objects are not in direct contact with each other, thatis, a case where another object is sandwiched therebetween. Accordingly,when it is described that a layer B is formed on (above) a layer A, itmeans either a case where the layer B is formed in direct contact withthe layer A, or a case where another layer (e.g., a layer C or a layerD) is formed in direct contact with the layer A, and then the layer B isformed in direct contact with the layer C or D. In addition, when it isdescribed that an object is formed over another object, it does notnecessarily mean that the object is in direct contact with anotherobject, and another object may be sandwiched therebetween. Accordingly,for example, when it is described that a layer B is formed over or abovea layer A, it means either a case where the layer B is formed in directcontact with the layer A, or a case where another layer (e.g., a layer Cor a layer D) is formed in direct contact with the layer A, and then thelayer B is formed in direct contact with the layer C or D. Similarly,when it is described that an object is formed below or under anotherobject, it means either a case where the objects are in direct contactwith each other or a case where the objects are not in contact with eachother.

The invention can provide a display device having an improved colorreproduction area on the CIE-XY chromaticity diagram in a display deviceusing light-emitting elements. In other words, the invention can providea display device which can express bright colors.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings,

FIG. 1 is a schematic diagram of a display device in the invention;

FIG. 2 is a schematic diagram of picture elements of a display device inthe invention;

FIG. 3 is a circuit diagram of picture elements of a display device inthe invention;

FIG. 4 is a circuit diagram of a pixel of a display device in theinvention;

FIG. 5 is a timing chart of a display device in the invention;

FIGS. 6A and 6B are cross-sectional views showing light-emittingelements of a display device of the invention;

FIGS. 7A to 7C are cross-sectional views of a display device in theinvention;

FIG. 8 is a diagram of emission spectrums of light-emitting elements;

FIG. 9 is a diagram of emission spectrums of light-emitting elements;

FIG. 10 is a diagram of emission spectrums of light-emitting elements;

FIG. 11 is a CIE-XY chromaticity diagram of light-emitting elements inthe invention;

FIGS. 12A and 12B are cross-sectional views of light-emitting elementsof a display device in the invention;

FIG. 13 is a diagram of emission spectrums of light-emitting elements;

FIGS. 14A and 14B are cross-sectional views of a display device in theinvention;

FIGS. 15A to 15C are cross-sectional views of a display device in theinvention;

FIG. 16 is a schematic diagram of picture elements of a display devicein the invention;

FIG. 17 is a schematic diagram of picture elements of a display devicein the invention;

FIG. 18 is a schematic diagram of picture elements of a display devicein the invention;

FIGS. 19A and 19B are schematic diagrams of picture elements of adisplay device in the invention;

FIG. 20 is a circuit diagram of pixels of a display device in theinvention;

FIG. 21 is a timing chart of a display device in the invention;

FIGS. 22A and 22B are timing charts of a display in the invention;

FIG. 23 is a circuit diagram of a pixel of a display device in theinvention;

FIG. 24 is a circuit diagram of a pixel of a display device in theinvention;

FIG. 25 is a diagram showing an operation of a transistor of a displaydevice in the invention;

FIG. 26 is a circuit diagram of picture elements of a display device inthe invention;

FIG. 27 is a top view of pixels of a display device in the invention;

FIG. 28 is a circuit diagram of picture elements of a display device inthe invention;

FIG. 29 is a circuit diagram of picture elements of a display device inthe invention;

FIGS. 30A and 30B are views of one mode of a display device in theinvention;

FIGS. 31A and 31B are views of one mode of a display device in theinvention;

FIGS. 32A and 32B are views of one mode of a display device in theinvention;

FIG. 33 is a view of an electronic device to which a display device ofthe invention can be applied;

FIG. 34 is a view of an electronic device to which a display device ofthe invention can be applied;

FIGS. 35A and 35B are views of electronic devices to which a displaydevice of the invention can be applied;

FIGS. 36A and 36B are views of electronic devices to which a displaydevice of the invention applied;

FIG. 37 is a view of an electronic device to which a display device ofthe invention applied;

FIGS. 38A to 38H are views of electronic devices to which a displaydevice of the invention can be applied;

FIG. 39 is a CIE-XY chromaticity diagram for illustrating a conventionaldisplay device;

FIGS. 40A and 40B are cross-sectional views of a display device in theinvention;

FIGS. 41A and 41B are cross-sectional views of a display device in theinvention;

FIGS. 42A and 42B are cross-sectional views of a display device in theinvention;

FIGS. 43A and 43B are cross-sectional views of a display device in theinvention;

FIGS. 44A to 44C are circuit diagrams of pixels of a display device inthe invention;

FIGS. 45A to 45C are cross-sectional views of light-emitting elements ofa display device in the invention;

FIG. 46 is a schematic diagram of a display device in the invention;

FIG. 47A is a top view of a display device, and FIGS. 47B and 47C arecross-sectional views thereof;

FIG. 48 is a cross-sectional view of a display device in the invention;

FIGS. 49A and 49B are cross-sectional views of a display device in theinvention;

FIG. 50 is a schematic view of a display device in the invention;

FIG. 51 is a cross-sectional view of a display device in the invention;

FIG. 52 is a circuit diagram of pixels of a display device in theinvention;

FIGS. 53A and 53B are schematic diagrams of picture elements of adisplay device in the invention;

FIGS. 54A and 54B are cross-sectional views of light-emitting elementsof a display device in the invention;

FIGS. 55A and 55B are views showing application examples of anelectronic device in the invention;

FIG. 56 is a view showing an application example of an electronic devicein the invention;

FIGS. 57A and 57B are views showing application examples of anelectronic device in the invention;

FIG. 58 is a view showing an application example of an electronic devicein the invention;

FIG. 59 is a view showing an application example of an electronic devicein the invention; and

FIG. 60 is a view showing an application example of an electronic devicein the invention.

DETAILED DESCRIPTION OF THE INVENTION

Although the invention will be fully described by embodiment modes andembodiments with reference to the drawings, it is to be understood thatvarious changes and modifications will be apparent to those skilled inthe art. Unless such changes and modifications depart from the scope ofthe invention, they should be construed as being included therein.Therefore, the invention is not limited to the following description.Note that the same portions or portions having the same function aredenoted by the same reference numerals, and repetitive description isomitted.

Embodiment Mode 1 Configuration of a Display Device in this EmbodimentMode

A configuration example of a display device in the invention is shown bya block diagram in FIG. 1. Reference numeral 100 denotes a pixel portionwhere a plurality of pixels 101 are arranged in matrix, and such aconfiguration is called an active matrix arrangement. In addition,reference numeral 102 denotes a signal line driver circuit and 103denotes a scan line driver circuit.

Note that the signal line driver circuit 102 and the scan line drivercircuit 103 are formed over the same substrate as a pixel portion 100 inFIG. 1; however, the configuration of the invention is not limited tothis. The signal line driver circuit 102 and the scan line drivercircuit 103 may be formed over a different substrate from the pixelportion 100, and connected to the pixel portion 100 with a connectorsuch as a flexible printed circuit (FPC). As a method for mounting theFPC, a connecting method using an anisotropic conductive material or ametal bump, or a wire bonding method can be employed. In addition, eachof the signal line driver circuit 102 and the scan line driver circuit103 is provided one by one in FIG. 1; however, the configuration of theinvention is not limited to this. The number of the signal line drivercircuit 102 and the scan line driver circuit 103 can be set arbitrarilyby a designer.

Note also that a pixel means an element having a color element formingone image, and includes a light-emitting element and an element whichdrives the light-emitting element (e.g., a circuit constructed fromtransistors) in this specification. In addition, a picture element meansan element having pixels each having a color element for displaying oneminimum image. Accordingly, in the case of a fall color display devicehaving color elements of R (Red), G (Green), and B (Blue), a pictureelement includes pixels including color elements of R, G and B. Further,with regard to a picture element which includes a plurality of pixels,pixels are called in such order that a first pixel and a second pixel.In addition, each pixel may have a different area dimension.

In this specification, a connection means an electrical connectionunless otherwise specified. On the other hand, a separation means astate where objects are not connected and electrically separated.

In addition, in FIG. 1, signal lines S1 to Sn, power supply lines V1 toVn, and scan lines G1 to Gm are provided in the pixel portion 100. Notethat the number of the signal lines and the scan lines is notnecessarily the same. Further, the pixel portion 100 is not necessarilyrequired to include all of the wires, and another wire may be providedtherein in addition to these wires.

The signal line driver circuit 102 may be any kind of circuits as longas it can supply an input signal to each of the signal lines S1 to Sn.In this embodiment mode, as a specific example, the signal line drivercircuit 102 includes a shift register 102 a, a first latch circuit 102b, and a second latch circuit 102 c. Note that the signal line drivercircuit 102 of a display device in the invention is not limited to theaforementioned configuration. In addition, the signal line drivercircuit 102 may be a signal line driver circuit which can process avideo signal in a digital form (also called a digital video signal or avideo signal), or a signal line driver circuit which outputs a videosignal in an analog form (an analog video signal) by using a D/A(Digital-Analog) converter circuit. Further, the signal line drivercircuit 102 may have a configuration including a level shifter circuit,a buffer circuit, or the like depending on the configurations of thedisplay device.

The scan line driver circuit 103 may be any kind of circuit as long asit can output a signal to each of the scan lines G1 to Gm in order toselect a pixel in the pixel portion 100. Specifically, the scan linedriver circuit 103 includes a shift register circuit in this embodimentmode. In addition, the scan line driver circuit 103 may have aconfiguration including a level shifter circuit, a buffer circuit, orthe like depending on the configurations of the display device. Further,the scan line driver circuit 103 may be constructed with a shiftregister and a sampling switch without using a latch circuit.

In addition, a clock signal (S_CLK), a clock inverted signal (S_CLKB), astart pulse (S_SP), a digital video signal (Digital Video Data), a latchsignal (Latch Signal), and the like are input to the signal line drivercircuit 102. Then, in accordance with the signals, a video signalcorresponding to pixels of each column is output to each of the signallines S1 to Sn. Note that an analog video signal may be input to thesignal line driver circuit 102.

Meanwhile, a clock signal (S_CLK), a clock inverted signal (S_CLKB), astart pulse (S_SP), and the like are input to the scan line drivercircuit 103. Then, in accordance with the signals, a signal whichselects pixels is output to a scan line Gi (one of the first scan linesG1 to Gm) of pixel columns which are selected.

Accordingly, the video signal input to the signal lines S1 to Sn iswritten to each column of the pixels 101 in a row selected by the signalwhich is input to the scan line Gi (one of the first scan lines G1 toGm) from the scan line driver circuit 103. Then, each pixel column isselected by each of the scan lines G1 to Gm and a video signalcorresponding to each pixel is written to each pixel. Then, each pixelholds the video signal that has been written for a certain period. Byholding the video signal for a certain period, each pixel can maintain astate of lighting or the like.

The display device using light-emitting elements shown in FIG. 1 isdescribed based on an active matrix driving method; however, theinvention is not limited to this. A simple (passive) matrix method mayalso be employed in the invention. The display device using the activematrix method shown in FIG. 1 includes a control circuit having a thinfilm transistor for switching in each pixel, and states of lighting andnon-lighting of each pixel are controlled by the control circuit in eachpixel. On the other hand, a display device using the simple (passive)matrix method is arranged such that a plurality of column signal linesand a plurality of row signal lines are crossed with each other, andlight-emitting elements are sandwiched at the crossed portion. Thus,when a potential difference is generated in a region which is sandwichedbetween a selected row signal line and a column signal line whichconducts the output operation, the light-emitting element emits lightwith a current flowing thereto.

A configuration of a display device using the passive matrix method isshown in FIG. 46. The display device shown in FIG. 46 includes a columnsignal line driver circuit 4601, a row signal line driver circuit 4602,and a pixel portion 4603. The pixel portion 4603 is provided with columnsignal lines S1 to Sn and row signal lines V1 to Vn, and has a pluralityof light-emitting elements 4604 between the column signals S1 to Sn andthe row signals V1 to Vn. In the case of employing the passive matrixmethod, the configurations of the invention can be simplified comparedwith the case of employing the active matrix method, and thus, it ispreferable.

The aforementioned configurations of the display device can be employedin the invention.

[Configuration of a Pixel in this Embodiment Mode]

A specific configuration of the pixel portion in the invention shown inFIG. 1 is shown in FIG. 2. In FIG. 2, each of a first pixel 201, asecond pixel 202, a third pixel 203, a fourth pixel 204, a fifth pixel205, and a sixth pixel 206 corresponds to the pixel 101 in FIG. 1. Inaddition, a picture element 200 which displays one minimum image isformed by combining the first pixel 201 to the sixth pixel 206. Each ofthe first pixel 201, the second pixel 202, the third pixel 203, thefourth pixel 204, the fifth pixel 205, and the sixth pixel 206 has alight-emitting element. A light-emitting element R1, a light-emittingelement R2, a light-emitting element G1, a light-emitting element G2, alight-emitting element B1, and a light-emitting element B2 are connectedto the first pixel 201, the second pixel 202, the third pixel 203, thefourth pixel 204, the fifth pixel 205, and the sixth pixel 206,respectively.

In this specification, the light-emitting element R1 of the first pixel201 and the light-emitting element R2 of the second pixel 202 havechromaticity whose x-coordinate in the CIE-XY chromaticity diagram is0.50 or more. In addition, the light-emitting element G1 of the thirdpixel 203 and the light-emitting element G2 of the fourth pixel 204 havechromaticity whose y-coordinate in the CIE-XY chromaticity diagram is0.55 or more. Further, the light-emitting element B1 of the fifth pixel205 and the light-emitting element B2 of the sixth pixel 206 havechromaticity whose x-coordinate and y-coordinate in the CIE-XYchromaticity diagram are 0.20 or less and 0.35 or less, respectively.More preferably, either one of the light-emitting element R1 of thefirst pixel 201 or the light-emitting element R2 of the second pixel 202has chromaticity whose x-coordinate and y-coordinate in the CIE-XYchromaticity diagram are 0.60 or more and 0.35 or less, respectively. Inaddition, more preferably, either one of the light-emitting element G1of the third pixel 203 or the light-emitting element G2 of the fourthpixel 204 has chromaticity whose x-coordinate and y-coordinate in theCIE-XY chromaticity diagram are 0.30 or less and 0.60 or more,respectively. In addition, more preferably, either one of thelight-emitting element B1 of the fifth pixel 205 or the light-emittingelement B2 of the sixth pixel 206 has chromaticity whose x-coordinateand y-coordinate in the CIE-XY chromaticity diagram are 0.15 or less and0.20 or less, respectively.

Note that in the invention, the absolute value G₁₂ which represents thedifference between the coordinates (the distance between the coordinatesof x and y) of the light-emitting element G1 and the light-emittingelement G2 in the CIE-XY chromaticity diagram is preferably larger thanthe absolute value R₁₂ which represents the difference between thecoordinates of the light-emitting element R1 and the light-emittingelement R2 in the CIE-XY chromaticity diagram, or the absolute value B₁₂which represents the difference between the coordinates of thelight-emitting element B1 and the light-emitting element B2 in theCIE-XY chromaticity diagram. By satisfying G₁₂>R₁₂ or G₁₂>B₁₂, the colorreproduction area can be improved to expand a color gamut which can beviewed by human eyes, and thus, it is preferable.

Note also that a region in the CIE-XY chromaticity diagram in thisspecification corresponds to a region showing visible light which can berecognized by human eyes. That is, a region in the CIE-XY chromaticitydiagram in this specification corresponds to an inner region surroundedby a thick line in the CIE-XY chromaticity diagram shown in FIG. 39.

In addition, the circuit configuration of the picture element 200 in theinvention shown in FIG. 2 is shown in FIG. 3. Each of the first pixel201, the second pixel 202, the third pixel 203, the fourth pixel 204,the fifth pixel 205, and the sixth pixel 206 shown in FIG. 2 includes asignal line S1 (one of the signal lines S1 to Sn), a scan line Gi (oneof the scan lines G1 to Gm), and a power supply line Vi (one of thepower supply lines V1 to Vn). In addition, each of the first pixel 201,the second pixel 202, the third pixel 203, the fourth pixel 204, thefifth pixel 205, and the sixth pixel 206 includes a first transistor 301for switching to control an input of a video signal, a second transistor302 for driving to decide the state of lighting or non-lighting of alight-emitting element by the video signal, a light-emitting element303, and a storage capacitor 304. The storage capacitor 304 is providedso as to hold a gate-source voltage (gate voltage) of the secondtransistor 302 more accurately; however, it is not necessarily required.Note that in this specification, voltage means a potential differencefrom a ground unless otherwise specified. In addition, thelight-emitting element 303 corresponds to the light-emitting elementsR1, R2, G1, G2, B1, and B2 in FIG. 2, and each light-emitting element isconnected to a circuit which drives the light-emitting element. In theconfiguration shown in FIG. 3, the power supply line can be shared tosupply currents to the light-emitting elements R1 and R2, thelight-emitting elements G1 and G2, or the light-emitting elements B1 andB2 by using the same power supply line Vi. Since the light-emittingelements R1 and R2, the light-emitting elements G1 and G2, and thelight-emitting elements B1 and B2 have almost the same tone of color,respectively, the light-emitting elements can share the power supplyline in this manner. As a result, the number of power supply linesdisposed in the display device can be reduced, which is preferable. InFIG. 3, power supply lines which are connected to the light-emittingelements R1 and R2, the light-emitting elements G1 and G2, and thelight-emitting elements B1 and B2, respectively, are described asdifferent wires; however, the power supply lines may be wires divergedfrom the same wire.

A configuration different from the configuration shown in FIG. 3 isshown in FIG. 52. In FIG. 52, a configuration having the same functionas that of FIG. 3 is denoted by the same reference numeral. As shown inFIG. 52, a configuration where the light-emitting elements R1 and R2,the light-emitting elements G1 and G2, and the light-emitting elementsB1 and B2 are connected to different second power supply lines Vi₂,respectively may be employed. By using the different power supply linesfor supplying currents to the light-emitting elements R1 and R2, thelight-emitting elements G1 and G2, and the light-emitting elements B1and B2, a voltage which is applied to the respective light-emittingelements can be controlled; thereby the luminance of each light-emittingelement can be controlled freely, and thus, it is preferable.

Here, a driving method of the light-emitting element 303 for obtaininglight emission in FIG. 3 is described with reference to FIG. 4. In FIG.4, a circuit connected to a light-emitting element 404 includes a firsttransistor 401 for switching to control an input of a video signal, asecond transistor 402 for driving to decide the light intensity of thelight-emitting element 404 by the video signal, a signal line 405, apower supply line 406, and a scan line 407. A gate of the firsttransistor 401 is connected to the scan line 407. One of either a firstterminal or a second terminal (a source or a drain) of the firsttransistor 401 is connected to the signal line 405 and the other isconnected to a gate of the second transistor 402. One of either a firstterminal or a second terminal of the second transistor 402 is connectedto the power supply line 406 and the other is connected to a pixelelectrode of the light-emitting element 404. The light-emitting element404 includes an anode and a cathode, and in this specification, in thecase where the anode is used as the pixel electrode, the cathode iscalled the opposite electrode; while in the case where the cathode isused as the pixel electrode, the anode is called the opposite electrode.Voltage of the opposite electrode is often kept at a constant level. Inaddition, the first transistor 401 and the second transistor 402 may beeither an n-channel transistor or a p-channel transistor. In the casewhere the anode is used as the pixel electrode and the cathode is usedas the opposite electrode, the second transistor 402 is preferably ap-channel transistor. On the other hand, in the case where the anode isused as the opposite electrode and the cathode is used as the pixelelectrode, the second transistor 402 is preferably an n-channeltransistor.

One of two electrodes of the storage capacitor 403 is connected to thegate of the second transistor 402. In addition, the other of the twoelectrodes of the storage capacitor 403 is connected to the power sourceline 406; however, the invention is not limited to this, and the otherof the two electrodes of the storage capacitor 403 may be connected toanother wire. The storage capacitor 403 is provided so as to hold agate-source voltage (gate voltage) of the second transistor 402 moreaccurately; however, it is not necessarily required by substituting thegate capacitance of the second transistor 402.

In FIG. 4, when the scan line 407 is selected in a period of writing,the first transistor 401 whose gate is connected to the scan line 407 isturned on. Then, the light-emitting element 404 emits light since acurrent flows from the power supply line 406 to the light-emittingelement 404 in accordance with a video signal input to the gate of thesecond transistor 402 from the signal line 405 through the firsttransistor 401.

Note that the pixel configuration is not limited to this. Various typesof pixel configurations can be applied such as a method for compensatingvariations of the threshold voltage of transistors and a method forinputting a signal current to the pixel.

The aforementioned pixel configurations can be employed in theinvention.

[Method of an Operation in this Embodiment Mode]

Timing of an operation at the time of displaying an image with thecircuit configuration shown in FIG. 4 is described with reference toFIG. 5. The display device conducts rewriting and displaying of imagesrepeatedly in a displaying period. The number of rewriting of images isgenerally set about 60 times per second so that a viewer does notperceive a flicker. Here, a period in which a series operation ofrewriting and displaying images is conducted once, that is, a periodshown by 501 in FIG. 5 is described as one frame period 501. In thisembodiment mode, a case where a 3-bit digital video signal is used in adigital time gray scale method is given as an example. In the case of adigital time gray scale method, the one frame period 501 is furtherdivided into a plurality of sub frame periods. Here, since a videosignal has 3 bits, the one frame period 501 is divided into three subframe periods, and writing and displaying images for each luminous colorare conducted in each period.

Each sub frame period includes an address (writing) period Ta# (# is anatural number) and a sustain (light-emitting) period Ts#. In FIG. 5,the length of the sustain (light-emitting) periods is Ts1:Ts2:Ts3=4:2:1,and 2³=8 gray scales are expressed by controlling the state of lightingor non-lighting of a light-emitting element in each sustain(light-emitting) period. That is, each sustain (light-emitting) periodis set to have a power-of-two length such thatTs1:Ts2:Ts3=2^((n-1)):2^((n-2)): . . . :2¹:2⁰. For example, in the casewhere a light-emitting element emits light only in Ts3, and alight-emitting element does not emit light in Ts1 and Ts2, lightemission is obtained only in about 14% of all of the sustain(light-emitting) periods. That is, luminance of about 14% can beexpressed. In the case where a light-emitting element emits light in Ts1and Ts2, and a light-emitting element does not emit light in Ts3, lightemission is obtained in about 86% of all of the sustain (light-emitting)periods. That is, luminance of about 86% can be expressed.

Each of the light-emitting elements R1, R2, G1, G2, B1, and B2 whichcorresponds to the light-emitting element 303 in FIG. 3 is driven bythis operation. In this manner, light-emitting periods of light-emittingelements which are provided in the respective pixels in the pictureelement 200 in FIG. 3 are controlled independently by circuits connectedto the respective light-emitting elements, and thus, a desired displaycolor can be obtained. Here, a display color means a color which can bevisually recognized as a mixed color where luminescences obtained from aplurality of light-emitting elements each having a different luminouscolor in one pixel are mixed.

Note that the driving method is not limited to this. When an analogsignal is input to the gate of the first transistor, luminance of thelight-emitting element 404 may be changed in an analog manner inresponse to the analog signal.

The aforementioned method of operation can be employed in the invention.

[Configuration of a Light-Emitting Element in the Invention]

Next, examples of light-emitting elements which can be applied to thedisplay device of the invention are shown in FIGS. 6A and 6B.

A light-emitting element shown in FIG. 6A has an element structure wherea substrate 601, an anode 602, a hole inject layer 603 which is made ofa hole inject material, a hole transport layer 604 which is made of ahole transport material, a light-emitting layer 605, an electrontransport layer 606 which is made of an electron transport material, anelectron inject layer 607 which is made of an electron inject material,and a cathode 608 are stacked in this order. Here, the light-emittinglayer 605 may be formed of only one kind of a light-emitting material ormay be formed of two or more kinds of light-emitting materials. Inaddition, the structure of the light-emitting element in the inventionis not limited to this. Needless to say, a circuit or a wire for drivinga light-emitting element which is constructed with a transistor may beprovided between the substrate 601 and the anode 602.

Further, in addition to the stacked structure shown in FIG. 6A whereeach functional layer is stacked, there are wide variations of elementstructures such as an element using a high molecular compound, and ahigh efficiency element which utilizes, as a light-emitting layer, atriplet light-emitting material which emits light in returning from atriplet excitation state. The light-emitting element can also be appliedto a white light-emitting element which can be obtained by controlling arecombination region of carries using a hole blocking layer and dividinga light-emitting region into two regions.

The element of the invention shown in FIG. 6A can be manufactured asfollows. First, a hole inject material, a hole transport material, and alight-emitting material are sequentially deposited over the substrate601 having the anode 602 (ITO: Indium Tin Oxide). Next, an electrontransport material and an electron inject material are deposited, andfinally the cathode 608 is formed by vapor-deposition.

Note that a hole generation layer may be provided instead of the holeinject layer. The hole generation layer means layer which generates ahole, and can be formed by mixing at least one material selected fromthe hole transport materials and a material showing anelectron-accepting property to the hole transport materials. Here, as ahole transport material, a material similar to a material which can beused for forming the hole transport material can be employed. Inaddition, as a material showing an electron-accepting property, metaloxide such as a molybdenum oxide, a vanadium oxide, a ruthenium oxide,or a rhenium oxide can be employed.

Next, materials suitable for the hole inject material, the holetransport material, the electron transport material, the electron injectmaterial, and the light-emitting material are described.

As the hole inject material, a phthalocyanine-based compound such asphthalocyanine (abbreviation: H₂Pc) or copper phthalocyanine(abbreviation: CuPc), a polymer such as a poly(polyethylenedioxythiophene)/poly(polystylene sulfonate) solution (abbreviation:PEDOT/PSS), or the like can be given. The hole inject layer can beformed by selecting a material with a hole transport property which hasa relatively lower ionization potential than an ionization potential ofa functional layer which is formed to be in contact with the oppositeside of an electrode functioning as an anode.

As a material which is most widely used as the hole transport material,4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviation: NPB),4,4′-bis[N-(3-methylphenyl)-N-phenylamino]biphenyl (abbreviation: TPD),4,4′,4″-tris(N,N-diphenylamino)triphenylamine (abbreviation: TDATA),4,4′,4″-tris[N-(3-methylphenyl)-N-phenylamino]triphenylamine(abbreviation: MTDATA), 4,4′-bis{N-[4-(N,N-di-m-tolylamino)phenyl]-N-phenylamino}biphenyl (abbreviation:DNTPD), 1,3,5-tris[N,N-di(m-tolyl)amino]benzene (abbreviation: m-MTDAB),4,4′,4″-tris(N-bazolyl)triphenylamine (abbreviation: TCTA),phthalocyanine (abbreviation: H₂Pc), copper phthalocyanine(abbreviation: CuPc), vanadyl phthalocyanine (abbreviation: VOPc), orthe like is given as an example. Alternatively, the hole transport layermay be a layer with a multilayer structure which is formed by combiningtwo or more layers made of the aforementioned materials.

As an electron transport material, in addition totris(8-quinolinolato)aluminum (abbreviation: Alq₃),tris(4-methyl-8-quinolinolato)aluminum (abbreviation: Almq₃),bis(10-hydroxybenzo[h]-quinolinato)beryllium (abbreviation: BeBq₂),bis(2-methyl-8-quinolinolato)(4-phenylphenolato)aluminum (abbreviation:BAlq), bis[2-(2′-hydroxypheyl)benzoxazolato]zinc (abbreviation:Zn(BOX)₂), bis[2-(2′-hydroxypheyl)benzothiazolato]zinc (abbreviation:Zn(BTZ)₂), or the like,2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (abbreviation:PBD), 1,3-bis[5-(4-tert-butylphenyl)-1,3,4-oxadiazol-2-yl]benzene(abbreviation: OXD-7),3-(4-biphenylyl)-4-phenyl-5-(4-tert-butylphenyl)-1,2,4-triazole(abbreviation: TAZ),3-(4-biphenylyl)-4-(4-ethylphenyl)-5-(4-tert-butylphenyl)-1,2,4-triazole(abbreviation: p-EtTAZ), bathophenanthroline (abbreviation: BPhen),bathocuproin (abbreviation: BCP),2,2′,2″-(1,3,5-benzenetriyl)-tris(1-phenyl-1H-benzimidazole)(abbreviation: TPBI), 4,4-bis(5-methylbenzoxazol-2-yl)stilbene(abbreviation: BzOs), or the like is given as an example. Alternatively,the electron transport layer may be a layer with a multilayer structurewhich is formed by combining two or more layers made of theaforementioned materials.

As an electron inject layer, an inorganic material such as alkalinemetal, alkaline earth metal, alkaline metal fluoride, alkaline earthmetal fluoride, alkaline metal oxide, or alkaline earth metal oxide isgiven as an example. In addition to the inorganic material, a materialwhich can be used for forming the electron transport layer such asBPhen, BCP, p-EtTAZ, TAZ, or BzOs can be employed as the material forforming the electron inject layer by selecting from the aforementionedmaterials a material having a higher electron affinity than the materialwhich is used for forming the electron transport layer. That is, theelectron inject layer can also be formed by selecting from materialshaving electron transport properties a material having relatively ahigher electron affinity in the electron inject layer than the electronaffinity in the electron transport layer.

As a light-emitting layer including a light-emitting material, amaterial which has excellent luminous efficiency and can emit light witha desired emission wavelength may be selected to be employed withoutlimiting to a certain light-emitting material. For example, in order toobtain red light emission, a material which presents light emissionhaving an emission spectrum with a peak of 600 to 680 nm such as4-dicyanomethylene-2-isopropyl-6-[2-(1,1,7,7-tetramethyl-9-julolidyl)ethenyl]-4H-pyran (abbreviation: DCJTI),4-dicyanomethylene-2-methyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran(abbreviation: DCJT),4-dicyanomethylene-2-tert-butyl-6-[2-(1,1,7,7-tetramethyl-9-julolidyl)ethenyl]-4H-pyran(abbreviation: DCJTB), periflanthene, or2,5-dicyano-1,4-bis(2-[10-methoxy-1,1,7,7-tetramethyl-9-julolidyl]ethenyl)benzenecan be employed. In addition, in order to obtain green-based lightemission, a material which presents light emission having an emissionspectrum with a peak of 500 to 550 nm such as N,N″-dimethylquinacridone(abbreviation: DMQd), Coumarin 6, Coumarin 545T, ortris(8-quinolinolato)aluminum (abbreviation: Alq₃) can be employed.Further, in order to obtain blue light emission, a material whichpresents light emission having an emission spectrum with a peak of 420to 500 nm such as 2-tert-butyl-9,10-di(2-naphthyl)anthracene(abbreviation: t-BuDNA), 9,10-diphenylanthracene (abbreviation: DPA),9,10-di(2-naphthyl) anthracene (abbreviation: DNA),bis(2-methyl-8-quinolinolato)-4-phenylphenolato-gallium (abbreviation:BGaq), or bis(2-methyl-8-quinolinolato)(4-phenylphenolato)aluminum(abbreviation: BAlq) can be employed. In addition to the aforementionedmaterials which emit fluorescence, materials which emit phosphorescencesuch as tris(2-phenylpyridine)iridium may also be employed.

A material used for making the light-emitting material into thedispersion state (also called a host material) is not limited to acertain material. In addition to a compound having an arylamine skeletonsuch as 4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviation:α-NPD), a carbazole derivative such as 4,4′-bis(N-carbazolyl)biphenyl(abbreviation: CBP) or 4,4′,4″-tri(N-carbazolyl)triphenylamine(abbreviation: TCTA), a metal complex such asbis[2-(2-hydroxyphenyl)pyridinato]zinc (abbreviation: Znpp₂),bis[2-(2′-hydroxypheyl)benzoxazolato]zinc (abbreviation: Zn(BOX)₂), ortris(8-quinolinolato)aluminum (abbreviation: Alq₃), or the like can beemployed.

In addition, as shown in FIG. 6B, a light-emitting element formed bystacking layers in reverse order from FIG. 6A can be employed. That is,the light-emitting element shown in FIG. 6B has an element structurewhere a substrate 601, a cathode 608, an electron inject layer 607 whichis made of an electron inject material, an electron transport layer 606which is made of an electron transport material, a light-emitting layer605, a hole transport layer 604 which is made of a hole transportmaterial, a hole inject layer 603 which is made of a hole injectmaterial, and an anode 602 are stacked in this order.

In order to extract light emission from the light-emitting element, atleast one of the anode and the cathode of the light-emitting elements isrequired to be transparent. A TFT and the light-emitting element areformed over a substrate; and there are light-emitting elements having atop emission structure where light emission is extracted through asurface on the side opposite to the substrate, having a bottom emissionstructure where light emission is extracted through a surface on thesubstrate side, and a dual emission structure where light emission isextracted through both the surface on the side opposite to the substrateand the surface on the substrate side. The pixel configuration of theinvention can be applied to the light-emitting elements having anyemission structure.

By combining materials having the respective functions as describedabove, the light-emitting elements of the invention can be manufactured.

[Configuration of an Emission Structure in the Display Device of thisEmbodiment Mode]

Next, examples of a top emission structure, a bottom emission structure,and a dual emission structure of light-emitting elements which can beapplied to the display device of the invention are shown FIGS. 7A to 7C.

A light-emitting element with the top emission structure is shown inFIG. 7A.

In the light-emitting element with the top emission structure, a drivingTFT 701 is formed over a substrate 700, a first electrode 702 is formedto be connected to a source electrode of the driving TFT 701, and alight-emitting layer 703 and a second electrode 704 are formed over thefirst electrode 702.

In addition, the first electrode 702 is an anode of the light-emittingelement while the second electrode 704 is a cathode of thelight-emitting element. That is, the portion where the light-emittinglayer 703 is sandwiched between the first electrode 702 and the secondelectrode 704 corresponds to the light-emitting element.

Further, as a material used for the first electrode 702 functioning asthe anode, a material having a high work function is preferablyemployed. For example, in addition to a single layer of a titaniumnitride film, a chromium film, a tungsten film, a Zn film, a Pt film, orthe like, stacked layers of a titanium nitride film and a filmcontaining aluminum as a main component, a three-layer structure of atitanium nitride film, a film containing aluminum as a main component,and a titanium nitride film can be employed. Note that with a stackedstructure, resistance as a wire is low, an excellent ohmic contact canbe obtained, and a function as an anode can also be obtained. By using ametal film which reflects light, an anode which does not transmit lightcan be obtained.

Furthermore, as a material used for the second electrode 704 functioningas the cathode, stacked layers of a thin metal film formed of a materialhaving a low work function (Al, Ag, Li, Ca, or an alloy of these such asMgAg, MgIn, AlLi, CaF₂, or calcium nitride) and a transparent conductivefilm (of ITO (Indium Tin Oxide), indium zinc oxide (IZO), zinc oxide(ZnO), or the like) is preferably employed. By using a thin metal filmand a transparent conductive film having transparency in this manner, acathode which can transmit light can be formed.

In this manner, light emitted from the light-emitting element can beextracted to the top surface as shown by an arrow in FIG. 7A.

In addition, the light-emitting element with the bottom emissionstructure is shown in FIG. 7B. Since the light-emitting element of thebottom emission structure is the same as the light-emitting element withthe structure in FIG. 7A other than the emission structure, descriptionis made with the same numerals as those in FIG. 7A.

Here, as a material used for the first electrode 702 functioning as theanode, a material having a high work function is desirably employed. Forexample, a transparent conductive film such as an ITO (Indium Tin Oxide)film or an indium zinc oxide (IZO) film can be employed. By using atransparent conductive film having transparency in this manner, an anodewhich can transmit light can be formed.

Further, as a material used for the second electrode 704 functioning asthe cathode, a metal film formed of a material having a low workfunction (Al, Ag, Li, Ca, or an alloy of these such as MgAg, Men, AlLi,CaF₂, or calcium nitride) can be used. By using a metal film whichreflects light in this manner, a cathode which does not transmit lightcan be obtained.

In this manner, light emitted from the light-emitting element can beextracted to the bottom surface as shown by an arrow in FIG. 7B.

The light-emitting element with the dual emission structure is shown inFIG. 7C. Since the light-emitting element with the dual emissionstructure is the same as the light-emitting element with the structurein FIG. 7A other than the emission structure, description is made withthe same numerals as those in FIG. 7A.

Here, as a material used for the first electrode 702 functioning as theanode, a material having a high work function is desirably employed. Forexample, a transparent conductive film such as an ITO (Indium Tin Oxide)film or an indium zinc oxide (IZO) film can be employed. By using atransparent conductive film having transparency in this manner, an anodewhich can transmit light can be formed.

In addition, as a material used for the second electrode 704 functioningas the cathode, stacked layers of a thin metal film formed of a materialhaving a low work function (Al, Ag, Li, Ca, or an alloy of these such asMgAg, MgIn, AlLi, CaF₂, or calcium nitride) and a transparent conductivefilm (of ITO (Indium Tin Oxide), indium oxide zinc oxide alloy(In₂O₃—ZnO), zinc oxide (ZnO), or the like) is preferably employed. Byusing a thin metal film and a transparent conductive film havingtransparency in this manner, a cathode which can transmit light can beformed.

In this manner, light emitted from the light-emitting element can beextracted to both the top and bottom surfaces as shown by arrows in FIG.7C.

The aforementioned emission structures can be employed for the displaydevice of the invention.

Further, in the emission structures shown in FIGS. 7A to 7C, anotheremission structure having more interlayer films can also be employed.

In FIG. 51A, a structure of a light-emitting element with a top emissionstructure is shown as an example. The structure shown in FIG. 51A isdifferent from FIG. 7A in that a single-layered interlayer insulatingfilm 5101 and a wire 5102 for being connected to a first electrode areprovided. By employing a film having planarity for the interlayerinsulating film 5101, disconnection of wires or the like due to steps ofthe interlayer film can be preferably reduced, for example, in the firstelectrode or the like provided over the interlayer insulating film 5101.

In addition, a structure where a first reflecting electrode 5103 whichis made of the same material as a gate electrode and a second reflectingelectrode 5104 which is made of the same material as source and drainelectrodes are provided below the light-emitting element is preferablyemployed. In the top emission structure, efficiency of light extractionis bad since light emitted below the light-emitting element is notemitted to the viewer's side. However, by employing a structure wherethe first reflecting electrode 5103 and the second reflecting electrode5104 are provided, more light can be emitted through the top surface ofthe light-emitting element, and thus, it is preferable.

The aforementioned emission structures can be employed for the displaydevice of the invention.

[Structure of a Light-Emitting Material in the Display Device in thisEmbodiment Mode]

Next, a specific example of a light-emitting material used for thelight-emitting element which can be applied to the display device of theinvention is described.

Description has been made of the configuration of the pixel portion ofthe invention where the picture element of the invention includes thefirst pixel, the second pixel, the third pixel, the fourth pixel, thefifth pixel, and the sixth pixel in FIG. 2. In addition, alight-emitting element is provided in each of the first pixel to thesixth pixel, such that the light-emitting element R1, the light-emittingelement R2, the light-emitting element G1, the light-emitting elementG2, the light-emitting element B1, and the light-emitting element B2 areconnected to the first pixel, the second pixel, the third pixel, thefourth pixel, the fifth pixel, and the sixth pixel, respectively.

In this specification, the light-emitting element R1 of the first pixeland the light-emitting element R2 of the second pixel of the inventionhave chromaticity whose x-coordinate in the CIE-XY chromaticity diagramis 0.50 or more. In addition, the light-emitting element G1 of the thirdpixel and the light-emitting element G2 of the fourth pixel of theinvention have chromaticity whose y-coordinate in the CIE-XYchromaticity diagram is 0.55 or more. Further, the light-emittingelement B1 of the fifth pixel and the light-emitting element B2 of thesixth pixel of the invention have chromaticity whose x-coordinate andy-coordinate in the CIE-XY chromaticity diagram are 0.15 or less and0.20 or less, respectively.

Note that a structure which satisfies the following conditions is morepreferable. Either one of the light-emitting element of the first pixelor the light-emitting element of the second pixel has chromaticity whosex-coordinate and y-coordinate in the CIE-XY chromaticity diagram are0.60 or more and 0.35 or less, respectively; either one of thelight-emitting element of the third pixel or the light-emitting elementof the fourth pixel has chromaticity whose x-coordinate and y-coordinatein the CIE-XY chromaticity diagram are 0.30 or less and 0.60 or more,respectively; either one of the light-emitting element of the fifthpixel or the light-emitting element of the sixth pixel has chromaticitywhose x-coordinate and y-coordinate in the CIE-XY chromaticity diagramare 0.15 or less and 0.20 or less, respectively. By arranging therespective color coordinates of the light-emitting elements provided inthe first pixel and the second pixel; the light-emitting elementsprovided in the third pixel and the fourth pixel; and the light-emittingelements provided in the fifth pixel and the sixth pixel in differentregions of the CIE-XY chromaticity diagram, a display device having amore improved color reproduction area on the CIE-XY chromaticity diagramcan be obtained.

Specific examples of the light-emitting elements R1 and R2 used for thefirst pixel and the second pixel of the invention are described.

A specific element structure of the light-emitting element R1 which isprovided in the first pixel is described. First, CuPu having a thicknessof 20 nm is formed as a hole inject layer over ITO having a thickness of110 nm; NPB having a thickness of 30 nm is formed as a hole transportlayer; a co-evaporation layer having a thickness of 30 nm is formed as alight-emitting layer, by co-evaporating2,3-bis(4-diphenylaminophenyl)quinoxaline (abbreviation: TPAQn) which isa host material andbis[2-(2′-benzothienyl)pyridinato-N,C3′]iridium(acetylacetonate)(abbreviation: Ir(btp)2(acac); BAlq having a thickness of 10 nm isformed as an electron transport layer; Alq having a thickness of 20 nmis formed; calcium fluoride having a thickness of 2 nm is formed as anelectron inject layer; and Al having a thickness of 150 nm is formed asa cathode sequentially. Note that the ratio of TPAQn to Ir(btp)2(acac)in the light-emitting layer is controlled so that Ir(btp)2(acac) has aconcentration of 8 wt %.

In addition, a specific element structure of the light-emitting elementR2 which is provided in the second pixel is described. First, CuPuhaving a thickness of 20 nm is formed as a hole inject layer over ITOhaving a thickness of 110 nm; NPB having a thickness of 30 nm is formedas a hole transport layer; a co-evaporation layer having a thickness of30 nm is formed as a light-emitting layer, by co-evaporating TPAQn whichis a host material and rubrene; BAlq having a thickness of 10 nm isformed as an electron transport layer; Alq having a thickness of 20 nmis formed; calcium fluoride having a thickness of 2 nm is formed as anelectron inject layer; and Al having a thickness of 150 nm is formed asa cathode sequentially. Note that the ratio of TPAQn to rubrene in thelight-emitting layer is controlled so that rubrene has a concentrationof 10 wt %.

FIG. 8 shows an emission spectrum 801 of the light-emitting element R1manufactured as above and an emission spectrum 802 of the light-emittingelement R2 manufactured as above. The emission spectrums in FIG. 8correspond to emission spectrums when current is supplied to thelight-emitting elements with a current density of 25 mA/cm². Theemission spectrum 802 of the light-emitting element R2 is located in aposition which is shifted to the short-wavelength side of the emissionspectrum 801 of the light-emitting element R1 in FIG. 8. At this time,chromaticity coordinates of the light-emitting element R1 on the CIE-XYchromaticity diagram are (x, y)=(0.68, 0.32). In addition, chromaticitycoordinates of the light-emitting element R2 on the CIE-XY chromaticitydiagram are (x, y)=(0.47, 0.52).

Next, specific examples of the light-emitting elements G1 and G2 usedfor the third pixel and the fourth pixel of the invention are described.

A specific element structure of the light-emitting element G1 which isprovided in the third pixel is described. DNTPD having a thickness of 50inn is formed as a hole inject layer over ITO having a thickness of 110nm; NPB having a thickness of 10 nm is formed as a hole transport layer;a co-evaporation layer having a thickness of 37.5 nm is formed as alight-emitting layer, by co-evaporating Alq which is a host material andCoumarin 6; Alq having a thickness of 37.5 nm is formed as an electrontransport layer; calcium fluoride having a thickness of 2 nm is formedas an electron inject layer; and Al having a thickness of 150 nm isformed as a cathode sequentially. Note that the ratio of Alq to Coumarin6 in the light-emitting layer is controlled so that Coumarin 6 has aconcentration of 0.3 wt %.

In addition, a specific element structure of the light-emitting elementG2 which is provided in the fourth pixel is described. DNTPD having athickness of 50 nm is formed as a hole inject layer over ITO having athickness of 110 nm; NPB having a thickness of 10 nm is formed as a holetransport layer; a co-evaporation layer having a thickness of 37.5 nm isformed as a light-emitting layer, by co-evaporating Alq which is a hostmaterial and DMQd; Alq having a thickness of 37.5 nm is formed as anelectron transport layer; calcium fluoride having a thickness of 2 nm isformed as an electron inject layer; and Al having a thickness of 150 nmis formed as a cathode sequentially. Note that the ratio of Alq to DMQdin the light-emitting layer is controlled so that DMQd has aconcentration of 0.3 wt %.

FIG. 9 shows an emission spectrum 901 of the light-emitting element G1manufactured as above and an emission spectrum 902 of the light-emittingelement G2 manufactured as above. The emission spectrums in FIG. 9correspond to emission spectrums when current supplied to thelight-emitting elements with a current density of 25 mA/cm². Theemission spectrum 902 of the light-emitting element G2 is located in aposition shifted to the long-wavelength side of the emission spectrum901 of the light-emitting element G1 in FIG. 9. At this time,chromaticity coordinates of the light-emitting element G1 on the CIE-XYchromaticity diagram are (x, y) (0.28, 0.63). In addition, chromaticitycoordinates of the light-emitting element G2 on the CIE-XY chromaticitydiagram are (x, y) (0.43, 0.56).

Next, specific examples of the light-emitting elements B1 and B2 usedfor the fifth pixel and the sixth pixel of the invention are described.

In addition, a specific element structure of the light-emitting elementB1 which is provided in the fifth pixel is described. DNTPD having athickness of 30 nm is formed as a hole inject layer over ITO having athickness of 110 nm; NPB having a thickness of 30 nm is formed as a holetransport layer; t-BuDNA having a thickness of 40 nm is formed as alight-emitting layer; Alq having a thickness of 20 nm is formed as anelectron transport layer; calcium fluoride having a thickness of 2 nm isformed as an electron inject layer; and Al having a thickness of 50 nmis formed as a cathode sequentially.

Further, a specific element structure of the light-emitting element B2which is provided in the sixth pixel is described. DNTPD having athickness of 30 nm is formed as a hole inject layer over ITO having athickness of 110 nm; NPB having a thickness of 30 nm is formed as a holetransport layer; a co-evaporation layer of 40 nm is formed as alight-emitting layer, by co-evaporating t-BuDNA and TPAQn; Alq having athickness of 20 nm is formed as an electron transport layer; calciumfluoride having a thickness of 2 nm is formed as an electron injectlayer; and Al having a thickness of 150 nm is formed as a cathodesequentially. Note that the ratio of t-BuDNA to TPAQ in thelight-emitting layer is controlled so TPAQn has a concentration of 5 wt%.

FIG. 10 shows an emission spectrum 1001 of the light-emitting element B1manufactured as above and an emission spectrum 1002 of thelight-emitting element B2 manufactured as above. The emission spectrumsin FIG. 10 correspond to emission spectrums when current is supplied tothe light-emitting elements with a current density of 25 mA/cm². Theemission spectrum 1002 of the light-emitting element B2 is located in aposition shifted to the long-wavelength side of the emission spectrum1001 of the light-emitting element B1 in FIG. 10. At this time,chromaticity coordinates of the light-emitting element B1 on the CIE-XYchromaticity diagram are (x, y)=(0.15, 0.11). In addition, chromaticitycoordinates of the light-emitting element B2 on the CIE-XY chromaticitydiagram are (x, y)=(0.18, 0.32).

FIG. 11 shows the CIE-XY chromaticity diagram and a diagram where eachcolor coordinate of the light-emitting elements R1, R2, G1, G2, B1, andB2 manufactured as above are plotted. In FIG. 11, a region where colorcoordinates of the light-emitting elements R1, G1, and B1 are connectedcorresponds to RGB1, while a region where color coordinates of thelight-emitting elements R2, G2, and B2 are connected corresponds toRGB2. By providing different tones of color of RGB which are thetrichromaticity of colors, colors with tones in a region surrounded byRGB6 can be expressed, and thus, a display device having an improvedcolor reproduction area on the CIE-XY chromaticity diagram can beprovided.

Note that in each light-emitting element, when the optical distancebetween a light-emitting region and a reflecting electrode (an electrodewhich reflects light) is L and a desired wavelength of light is λ, aso-called micro resonator structure (a micro cavity structure) whichsatisfies L=(2m−1)λ/4 (note that in is a natural number not less than 1)can be employed in order to increase the color purity.

Note also that any one of the color coordinates of the light-emittingelements R2, G2, and B2 is only required to be located outside theregion where color coordinates of the light-emitting elements R1, G1,and B1 are connected. This is because if all of the light-emittingelements R2, G2, and B2 have color coordinates inside the region wherecolor coordinates of the light-emitting elements R1, G1, and B1 areconnected, color reproduction areas of RGB1 and RGB2 overlap with eachother.

As described above, the display device of the invention can employ theaforementioned materials of the light-emitting elements in each pixel.Note that the aforementioned materials of the light-emitting elementsare only illustrative, and therefore, any light-emitting element can beemployed as long as it has similar color coordinates to those of theinvention.

Note that this embodiment can be freely combined with the otherembodiment modes or embodiments in this specification.

Embodiment Mode 2

In this embodiment mode, a different configuration of light-emittingelements from the configuration of the light-emitting elements in thedisplay of the invention in the aforementioned embodiment mode isdescribed.

Description has been made of the configuration of the pixel portion ofthe invention with reference to FIG. 2 where the picture element of theinvention includes the first pixel, the second pixel, the third pixel,the fourth pixel, the fifth pixel, and the sixth pixel. In addition, alight-emitting element is provided in each of the first pixel to thesixth pixel, so that a light-emitting element R1, a light-emittingelement R2, a light-emitting element G1, a light-emitting element G2, alight-emitting element B1, and a light-emitting element B2 are connectedto the first pixel, the second pixel, the third pixel, the fourth pixel,the fifth pixel, and the sixth pixel, respectively.

In this specification, the light-emitting element R1 in the first pixeland the light-emitting element R2 in the second pixel of the inventionin this specification have chromaticity whose x-coordinate in the CIE-XYchromaticity diagram is 0.50 or more. In addition, the light-emittingelement G1 in the third pixel and the light-emitting element G2 in thefourth pixel of the invention have chromaticity whose y-coordinate inthe CIE-XY chromaticity diagram is 0.55 or more. Further, thelight-emitting element B1 in the fifth pixel and the light-emittingelement B2 in the sixth pixel of the invention have chromaticity whosex-coordinate and y-coordinate in the CIE-XY chromaticity diagram is 0.15or less and 0.20 or less, respectively.

In this embodiment mode, the light-emitting elements R1 and R2 providedin the first and second pixels are formed to have different emissionspectrums from each other; the light-emitting elements G1 and G2provided in the third and fourth pixels are formed to have differentemission spectrums from each other, and the light-emitting elements B1and B2 provided in the fifth and sixth pixels are formed to havedifferent emission spectrums from each other, by varying the thicknessof the respective light-emitting elements. Accordingly, the colorcoordinates on the CIE-XY chromaticity diagram are varied between thelight-emitting elements R1 and R2 provided in the first and secondpixels, between the light-emitting elements G1 and G2 provided in thethird and fourth pixels, and between the light-emitting elements B1 andB2 provided in the fifth and sixth pixels, respectively. A specificexample is shown below.

In this embodiment mode, a specific example for varying coordinates ofthe CIE-XY chromaticity diagram between the light emitting-element G1and the light-emitting element G2 used for the third pixel and thefourth pixel is described.

A specific structure of the light-emitting element G1 provided in thethird pixel is described. CuPc of having a thickness of 20 nm is formedas a hole inject layer over ITO having a thickness of 110 nm; NPB havinga thickness of 40 nm is formed as a hole transport layer; aco-evaporation layer of 40 nm is formed as a light-emitting layer, byco-evaporating Alq which is a host material and Coumarin 6 which is agreen light-emitting material; a co-evaporation layer having a thicknessof 30 snm is formed as an electron inject layer, by co-evaporating Alqand Li; and Al having a thickness of 150 nm is formed as a cathodesequentially. Note that the ratio of Alq to Coumarin 6 in thelight-emitting layer is controlled so that Coumarin 6 has aconcentration of 0.3 wt %. In addition, the ratio of Alq to Li in theelectron inject layer is controlled so that Li has a concentration of 1wt %.

A stacked structure of the light-emitting element G1 provided in thethird pixel is shown in FIG. 12A. The light-emitting element G1 has anelement structure where a substrate 1211, an anode 1213 formed thereoverwith a transistor 1212 sandwiched therebetween, a hole inject layer1201A which is made of a hole inject material, a hole transport layer1202A which is made of a hole transport material, a light-emitting layer1203A, an electron transport layer 1204A which is made of an electrontransport material, an electron inject layer 1205A which is made of anelectron inject material, and a cathode 1214 are stacked in this order.Note that a stacked structure in a right view of FIG. 12A corresponds toan enlarged cross-sectional view of the light-emitting element portionin FIG. 12A.

A specific structure of the light-emitting element G2 provided in thefourth pixel is described. CuPc having a thickness of 20 nm is formed asa hole inject layer over ITO having a thickness of 110 nm; NPB having athickness of 40 nm is formed as a hole transport layer, a co-evaporationlayer having a thickness of 40 nm is formed as a light-emitting layer,by co-evaporating Alq which is a host material and Coumarin 6 which is agreen light-emitting material; a co-evaporation layer having a thicknessof 30 nm is formed as an electron inject layer, by co-evaporating Alqand Li; a co-evaporation layer having a thickness of 180 nm is formed,by co-evaporating NPB and molybdenum oxide (VI); and Al having athickness of 150 nm is formed as a cathode sequentially. Note that theratio of Alq to Coumarin 6 in the light-emitting layer is controlled sothat Coumarin 6 has a concentration of 0.3 wt %. In addition, the ratioof Alq to Li in the electron inject layer is controlled so that Li has aconcentration of 1 wt %. Note that the ratio of NPB to molybdenum oxide(VI) is controlled so that molybdenum oxide has a concentration of 20 wt%.

A stacked structure of the light-emitting element G2 provided in thefourth pixel is shown in FIG. 12B. The light-emitting element G2 has anelement structure where a substrate 1211, an anode 1213 formed thereoverwith a transistor 1212 sandwiched therebetween, a hole inject layer1201B which is made of a hole inject material, a hole transport layer1202B which is made of a hole transport material, a light-emitting layer1203B, an electron transport layer 1204B which is made of an electrontransport material, the electron inject layer 1205B which is made of anelectron inject material, a co-evaporation layer of NPB and molybdenumoxide (VI) 1206, and a cathode 1214 are stacked in this order. Note thata stacked structure in a right view of FIG. 12B corresponds to anenlarged cross-sectional view of the light-emitting element portion inFIG. 12B.

In addition, FIG. 13 shows an emission spectrum 1301 of thelight-emitting element G1 which is stacked as shown in FIG. 12A, and anemission spectrum 1302 of the light-emitting element G2 which is stackedas shown in FIG. 12B. The emission spectrums in FIG. 13 correspond toemission spectrums when current is supplied to the light-emittingelements with a current density of 25 mA/cm². The emission spectrum 1302of the light-emitting element G2 is located in a position shifted to theshort-wavelength side of the emission spectrum 1301 of thelight-emitting element G1 in FIG. 13. At this time, chromaticitycoordinates of the light-emitting element G1 on the CIE-XY chromaticitydiagram are (x, y)=(0.30, 0.64). In addition, chromaticity coordinatesof the light-emitting element G2 on the CIE-XY chromaticity diagram are(x, y)=(0.21, 0.69).

Similarly, the light-emitting elements R1 and R2 provided in the firstand second pixels can be formed to have different emission spectrumsfrom each other; and the light-emitting elements B1 and B2 provided inthe fifth and sixth pixels can be formed to have different emissionspectrums from each other, by varying the thickness of the respectivelight-emitting elements. In other words, the color coordinates on theCIE-XY chromaticity diagram can be varied between the light-emittingelements R1 and R2 provided in the first and second pixels, and betweenthe light-emitting elements B1 and B2 provided in the fifth and sixthpixels.

Like an example shown in this embodiment mode, the light-emittingelements R1 and R2 provided in the first and second pixels can be formedto have different color coordinates from each other on the CIE-XYchromaticity diagram as well as the light-emitting elements B1 and B2provided in the fifth and sixth pixels can be formed to have differentcolor coordinates from each other on the CIE-XY chromaticity diagram, byvarying the thickness of the respective light-emitting element. Needlessto say, by using different materials for the respective light-emittingelements while at the same time varying the thickness of the respectivelight-emitting elements, light-emitting elements having different colorcoordinates from each other on the CIE-XY chromaticity diagram may beobtained.

Furthermore, varying the emission spectrums by varying the thickness ofthe respective light-emitting elements (thickening) is not limited to beachieved by forming a co-evaporation layer. For example, as shown inFIGS. 45A to 45C and FIGS. 54A and 54B, varying the emission spectrumsby varying the thickness of the respective light-emitting elements maybe achieved by thickening any of a hole inject layer 1201, a holetransport layer 1202, a light-emitting layer 1203, an electron transportlayer 1204, or an electron inject layer 1205. For example, as shown inFIG. 45A, by thickening the hole inject layer 1201, the thickness as awhole may be varied between the light-emitting elements R1 and R2,between the light-emitting elements G1 and G2, and between thelight-emitting elements B1 and B2. Alternatively, as shown in FIG. 45B,by thickening the hole transport layer 1202, the thickness as a wholemay be varied between the light-emitting elements R1 and R2, between thelight-emitting elements G1 and G2, and between the light-emittingelements B1 and B2. Further alternatively, as shown in FIG. 45C, bythickening the light-emitting layer 1203, the thickness as a whole maybe varied between the light-emitting elements R1 and R2, between thelight-emitting elements G1 and G2, and between the light-emittingelements B1 and B2. In addition, as shown in FIG. 54A, by thickening theelectron transport layer 1204, the thickness as a whole may be variedbetween the light-emitting elements R1 and R2, between thelight-emitting elements G1 and G2, and between the light-emittingelements B1 and B2. Further, as shown in FIG. 54B, by thickening theelectron inject layer 1205, the thickness as a whole may be variedbetween the light-emitting elements R1 and R2, between thelight-emitting elements G1 and G2, and between the light-emittingelements B1 and B2. Needless to say, by thickening a plurality of filmsamong the hole inject layer, the hole transport layer, thelight-emitting layer, the electron transport layer, and the electroninject layer to vary the film thickness, light-emitting elements havingdifferent color coordinates from each other on the CIE-XY chromaticitydiagram may be obtained.

Note that in order to achieve the thickening of the film, aco-evaporation layer including metal oxide is employed in thisembodiment mode. By employing metal oxide for the co-evaporation layer,increase in driving voltage due to thickening of the film can beprevented, and thus, it is preferable.

Note that this embodiment mode in the invention is different from theso-called micro resonator structure (the micro cavity structure) whichsatisfies L=(2m−1)λ/4 (note that m is a natural number not less than 1)where the optical distance between a light-emitting region and areflecting electrode (an electrode which reflects light) is L and adesired wavelength of light is λ. Note also that the optical distance iscalculated by the following formula: “the actual distance×the refractiveindex at wavelength λ”. The optical distance of the light-emittingelement of this embodiment mode in the invention may be designed in anymanner as long as the light-emitting elements R1 and R2 have differentemission spectrums from each other, the light-emitting elements G1 andG2 have different emission spectrums from each other, and thelight-emitting elements B1 and B2 have different emission spectrums fromeach other. For example, the light-emitting elements may be designed tobe thinner in ascending order from the light-emitting element R1, thelight-emitting, element R2, the light-emitting element G1, thelight-emitting element G2, the light-emitting element B1, and thelight-emitting element B2. Alternatively, the light-emitting elementsmay also be designed to be thinner in ascending order from thelight-emitting elements R1 and R2, the light-emitting elements G1 andG2, and the light-emitting elements B1 and B2.

Note also that by thickening the films of the light-emitting elements,the distance D between a first electrode (an anode) and a secondelectrode (a cathode) of the light-emitting element varies between thelight-emitting elements R1 and R2, between the light-emitting elementsG1 and G2, and between the light-emitting elements B1 and B2,respectively in this embodiment mode. In this specification, thedistance D between the first electrode (the anode) and the secondelectrode (the cathode) of the light-emitting element corresponds to thedistance between an end face of the first electrode on thelight-emitting layer side and an end face of the second electrode on thelight-emitting layer side (a boundary of the first electrode on the holeinject layer, and a boundary of the second electrode on the electroninject layer in this embodiment mode).

As described above, the display device of the invention can employ theaforementioned materials of the light-emitting elements in each pixel.Note that the aforementioned materials of the light-emitting elementsare only illustrative; therefore, any light-emitting element can beemployed as long as it has a similar color coordinate to that of theinvention.

Note that this embodiment can be freely combined with the otherembodiment modes or embodiments in this specification.

Embodiment Mode 3

In this embodiment mode, a different configuration of light-emittingelements from the configuration of the light-emitting elements in thedisplay of the invention in the aforementioned embodiment modes isdescribed.

Description has been made of the configuration of the pixel portion ofthe invention where the picture element of the invention includes thefirst pixel, the second pixel, the third pixel, the fourth pixel, thefifth pixel, and the sixth pixel in FIG. 2 In addition, a light-emittingelement is provided in each of the first pixel to the sixth pixel, suchthat a light-emitting element R1, a light-emitting element R2, alight-emitting element G1, a light-emitting element G2, a light-emittingelement B1, and a light-emitting element B2 are connected to the firstpixel, the second pixel, the third pixel, the fourth pixel, the fifthpixel, and the sixth pixel, respectively.

In this specification, the light-emitting element R1 of the first pixeland the light-emitting element R2 of the second pixel of the inventionhave chromaticity whose x-coordinate in the CIE-XY chromaticity diagramis 0.50 or more. In addition, the light-emitting element G1 of the thirdpixel and the light-emitting element G2 of the fourth pixel of theinvention have chromaticity whose y-coordinate in the CIE-XYchromaticity diagram is 0.55 or more. Further, the light-emittingelement B1 of the fifth pixel and the light-emitting element B2 of thesixth pixel of the invention have chromaticity whose x-coordinate andy-coordinate in the CIE-XY chromaticity diagram are 0.15 or less and0.20 or less, respectively.

In this embodiment mode, the light-emitting elements R1 and R2 providedin the first and second pixels are formed to have roughly equal emissionspectrums to each other, the light-emitting elements G1 and G2 providedin the third and fourth pixels are formed to have roughly equal emissionspectrums to each other, and the light-emitting elements B1 and B2provided in the fifth and sixth pixels are formed to have roughly equalemission spectrums to each other. By providing a color filter at aportion through which light emitted from each of the light-emittingelements travels, the color coordinates on the CIE-XY chromaticitydiagram are varied between the light-emitting elements R1 and R2provided in the first and second pixels, between the light-emittingelements G1 and G2 provided in the third and fourth pixels, and betweenthe light-emitting elements B1 and B2 provided in the fifth and sixthpixels. A specific example is shown below.

In this embodiment mode, a configuration of a display device isdescribed using a cross-sectional structure of a picture elementportion.

FIGS. 14A and 14B are partial cross-sectional views of a picture elementof the display device in this embodiment mode. The display device of theinvention shown in FIG. 14A includes a substrate 1400, a base insulatingfilm 1401, a semiconductor layer 1402, a gate insulating film 1403, agate electrode 1404, an interlayer insulating film 1405, a connectingportion 1406, a first electrode 1407 of a light-emitting element, apartition wall 1408, a light-emitting layer 1409, a second electrode1410 of the light-emitting element, a color filter (R1) 1411, a colorfilter (R2) 1412, a color filter (G1) 1413, a color filter (G2) 1414, acolor filter (B1) 1415, a color filter (B2) 1416, and an oppositesubstrate 1417.

The light emitting-element is formed at a portion where thelight-emitting layer 1409 is sandwiched between the first electrode 1407and the second electrode 1410 of the light-emitting element. Thelight-emitting element is connected to a thin film transistor which ismade of the semiconductor layer 1402, the gate insulating film 1403, andthe gate electrode 1404 through the connecting portion 1406 which iselectrically in contact with the first electrode 1407 of thelight-emitting element to be controlled light emission. In addition,this embodiment mode shows a structure where the first electrode 1407 isa reflecting electrode formed of a highly reflective material, and thesecond electrode 1410 is a transparent electrode formed of a conductivematerial having a light transmitting property, so that light isextracted from the direction of the second electrode 1410.

Note that the thin film transistors in FIG. 14A drive the light-emittingelement R1, the light-emitting element R2, the light-emitting elementG1, the light-emitting element G2, the light-emitting element B1, andthe light-emitting element B2, respectively, in order from left toright. Note that emission spectrums of the light-emitting elements inthe case where the color filter are not provided in the respectivepixels are roughly equal between the light-emitting elements R1 and R2,between the light-emitting elements G1 and G2, and between thelight-emitting elements B1 and B2. Note also that arrows shown in FIG.14A schematically show the light emitted through the color filters fromthe light-emitting element R1, the light-emitting element G1, thelight-emitting element B1, the light-emitting element R2, thelight-emitting element G2, and the light-emitting element B2,respectively, in order from left to right.

In this embodiment mode, the color filter (R1) 1411, the color filter(R2) 1412, the color filter (G1) 1413, the color filter (G2) 1414, thecolor filter (B1) 1415, and the color filter (B2) 1416 are provided atlight-emission sides of the light-emitting elements R1 and R2 providedin the first and second pixels, the light-emitting elements G1 and G2provided in the third and fourth pixels, and the light-emitting elementsB1 and B2 provided in the fifth and sixth pixels, respectively. In thisembodiment mode, by varying transmission properties of the color filter(R1) 1411 and the color filter (R2) 1412 from each other, varyingtransmission properties of the color filter (G1) 1413 and the colorfilter (G2) 1414 from each other, and varying transmission properties ofthe color filter (B1) 1415 and the color filter (B2) 1416 from eachother to vary emission spectrums of the light emitted from thelight-emitting elements R1 and R2 from each other, vary emissionspectrums of the light emitted from the light-emitting elements G1 andG2 from each other, and vary emission spectrums of the light emittedfrom the light-emitting elements B1 and B2 from each other,light-emitting elements each having a different color coordinate on theCIE-XY chromaticity diagram can be obtained.

Note that the color filters may be manufactured by any of a pigmentdispersion method, a printing method, an electrodeposition method, and astaining method. The light-emitting elements R1 and R2 provided in thefirst and second pixels, the light-emitting elements G1 and G2 providedin the third and fourth pixels, and the light-emitting elements B1 andB2 provided in the fifth and sixth pixels may be light-emitting elementshaving the same emission spectrum, for example, a light-emitting elementhaving an emission spectrum which emits white light. By providing thelight-emitting elements having the same emission spectrum, a process ofproducing the light-emitting elements can be simplified, and thus, it ispreferable.

FIG. 14B is a partial cross-sectional view of a picture element of thedisplay device in this embodiment mode. Note that each structure of thedisplay device in the invention shown in FIG. 14B conforms to FIG. 14A.

What is different from FIG. 14A is that light emitted from thelight-emitting element R1, the light-emitting element G1, and thelight-emitting element B1 does not travel through the color filters.Emission spectrums of the light-emitting elements in the case where thecolor filters are not provided in the respective pixels at this time areroughly equal between the light-emitting elements R1 and R2, between thelight-emitting elements G1 and G2, and between the light-emittingelements B1 and B2. In FIG. 14B, emission spectrums of light emittedfrom the light-emitting element R2, the light-emitting element G2, andthe light-emitting element B2 are varied by the transmission propertiesof the color filter (R2) 1412, the color filter (G2) 1414, and the colorfilter (B2) 1416. Accordingly, by varying the emission spectrums oflight emitted from the light-emitting elements R1 and R2 from eachother, varying emission spectrums of light emitted from thelight-emitting elements G1 and G2 from each other, and varying emissionspectrums of light emitted from the light-emitting elements B1 and B2from each other, light-emitting elements each having a different colorcoordinate on the CIE-XY chromaticity diagram can be obtained.

Note that by disposing the same color light-emitting elements over thewhole surface, varying emission spectrums of light emitted from thelight-emitting elements R1 and R2 from each other, varying emissionspectrums of light emitted from the light-emitting elements G1 and G2from each other, and varying emission spectrums of light emitted fromthe light-emitting elements B1 and B2 from each other through colorfilters each having a different transmission property, light-emittingelements each having a different color coordinate on the CIE-XYchromaticity diagram may be obtained. For example, white light-emittingelements are disposed as the same color light-emitting elements, andcolor filters may be disposed above the first pixel to the sixth pixelas shown in FIG. 14A.

In addition, FIG. 15A is a view showing a display device of theinvention having a different structure from FIG. 14A. Note that eachstructure of the display device in the invention shown in FIG. 15Aconforms to FIG. 14A. In FIG. 15A, an example of a bottom emissiondisplay device having a structure where the light-emitting element emitslight to the first electrode 1407 side thereof is shown. In FIG. 15B,the first electrode 1407 is formed of a conductive material having alight transmitting property in order to extract light emission from thefirst electrode 1407 side, and the second electrode 1410 is formed as areflecting electrode which is manufactured by using a highly reflectiveconductive material.

In this embodiment mode, the light-emitting elements R1 and R2 providedin the first and second pixels, the light-emitting elements G1 and G2provided in the third and fourth pixels, and the light-emitting elementsB1 and B2 provided in the fifth and sixth pixels, the color filter (R1)1411, the color filter (R2) 1412, the color filter (G1) 1413, the colorfilter (G2) 1414, the color filter (31) 1415, and the color filter (B2)1416 are provided, respectively at light-emission sides of thelight-emitting elements R1 and R2 provided in the first and secondpixels, the light-emitting elements G1 and G2 provided in the third andfourth pixels, and the light-emitting elements B1 and B2 provided in thefifth and sixth pixels. In this embodiment mode, by varying transmissionproperties of the color filter (R1) 1411 and the color filter (R2) 1412from each other, varying transmission properties of the color filter(G1) 1413 and the color filter (G2) 1414 from each other, and varyingtransmission properties of the color filter (B1) 1415 and the colorfilter (B2) 1416 from each other to vary emission spectrums of lightemitted from the light-emitting elements R1 and R2 from each other, varyemission spectrums of light emitted from the light-emitting elements G1and G2 from each other, and vary emission spectrums of light emittedfrom the light-emitting elements B1 and B2 from each other,light-emitting elements each having a different color coordinate on theCIE-XY chromaticity diagram can be obtained.

Note that the color filters may be manufactured by any of a pigmentdispersion method, a printing method, an electrodeposition method, and astaining method. Each of the light-emitting elements R1 and R2 providedin the first and second pixels, the light-emitting elements G1 and G2provided in the third and fourth pixels, and the light-emitting elementsB1 and B2 provided in the fifth and sixth pixels may be a light-emittingelement including a light-emitting element having the same emissionspectrum, for example, a light-emitting element having an emissionspectrum which emits white light. By including the light-emittingelement having the same emission spectrum, a process of producing thelight-emitting element can be simplified, and thus, it is preferable.

FIG. 15B is a partial cross-sectional view of a picture element of thedisplay device in this embodiment mode. Note that each structure of thedisplay device in the invention shown in FIG. 15B conforms to FIG. 15A.

What is different from FIG. 15A is that light emitted from thelight-emitting element R1, the light-emitting element G1, and thelight-emitting element B1 does not travel through the color filters.Emission spectrums of light emitted from the light-emitting elements inthe case where the color filters are not provided in the respectivepixels at this time are roughly equal between the light-emittingelements R1 and R2, between the light-emitting elements G1 and G2, andbetween the light-emitting elements B1 and B2. In FIG. 15B, emissionspectrums of light emitted from the light-emitting element R2, thelight-emitting element G2, and the light-emitting element B2 are variedby the transmission properties of the color filter (R2) 1412, the colorfilter (G2) 1414, and the color filter (B2) 1416. Accordingly, byvarying the emission spectrums of light emitted from the light-emittingelements R1 and R2 from each other, varying the emission spectrums oflight emitted from the light-emitting elements G1 and G2 from eachother, and varying the emission spectrums of light emitted from thelight-emitting elements B1 and B2 from each other, light-emittingelements each having a different color coordinate on the CIE-XYchromaticity diagram can be obtained.

Note that by disposing the same color light-emitting elements over thewhole surface, and providing color filters each having a differenttransmission property so as to overlap with the light-emitting elements,so that emission spectrums of light emitted from the light-emittingelements R1 and R2 are varied from each other, emission spectrums oflight emitted from the light-emitting elements G1 and G2 are varied fromeach other, and emission spectrums of light emitted from thelight-emitting elements B1 and B2 are varied from each other through thecolor filters, light-emitting elements each having a different colorcoordinate on the CIE-XY chromaticity diagram may be obtained. Forexample, white light-emitting elements are disposed as the same colorlight-emitting elements, and color filters may be disposed above thefirst pixel to the sixth pixel as shown in FIG. 15A.

FIG. 15C is a partial cross-sectional view of a picture element of thedisplay device in this embodiment mode. Note that each structure of thedisplay device in the invention shown in FIG. 15C conforms to FIGS. 15Aand 15B.

What is different from FIGS. 15A and 15B is that the color filter (R1)1411, the color filter (R2) 1412, the color filter (G1) 1413, the colorfilter (G2) 1414, the color filter (B1) 1415, and the color filter (B2)1416 are disposed below the first electrode 1407 which is disposedbetween the light-emitting element and a transistor. Thus, the processcan be simplified, and thus, it is easy to conduct. Accordingly, byvarying the emission spectrums of light emitted from the light-emittingelements R1 and R2 from each other, varying the emission spectrums oflight emitted from the light-emitting elements G1 and G2 from eachother, and varying the emission spectrums of light emitted from thelight-emitting elements B1 and B2 from each other, light-emittingelements each having a different color coordinate on the CIE-XYchromaticity diagram can be obtained.

In addition, by varying the emission spectrums of light emitted from thelight-emitting elements R1 and R2 from each other, varying the emissionspectrums of light emitted from the light-emitting elements G1 and G2from each other, and varying the emission spectrums of light emittedfrom the light-emitting elements B1 and B2 from each other, using amethod where a short-wavelength monochromatic light-emitting element isdisposed and a luminous color thereof is converted into a required colorthrough a color conversion layer, light-emitting elements each having adifferent color coordinate on the CIE-XY chromaticity diagram may beobtained. The display device of the invention shown in FIG. 40A includesa substrate 4000, a base insulating film 4001, a semiconductor layer4002, a gate insulating film 4003, a gate electrode 4004, an interlayerinsulating film 4005, a connecting portion 4006, a first electrode 4007of a light-emitting element, a partition wall 4008, light-emittinglayers 4009A and 4009B, a second electrode 4010 of the light-emittingelement, a color conversion layer (R1) 4011, a color conversion layer(G1) 4012, a color conversion layer (R2) 4013, a color conversion layer(G2) 4014, and an opposite substrate 4015.

For example, blue light-emitting elements B1 and B2 each having adifferent emission spectrum are disposed as the light-emitting layers4009A and 4009B which emit short-wavelength monochromatic light, and inthe case of a top emission structure as shown in FIG. 40A, the colorconversion layers may be disposed above the first pixel, the secondpixel, the fourth pixel, and the fifth pixel. Alternatively, in the caseof a bottom emission structure, blue light-emitting elements B1 and B2each having a different emission spectrum are disposed as thelight-emitting layers 4009A and 4009B which emit short-wavelengthmonochromatic light, and the color conversion layers may be disposedbelow the first pixel, the second pixel, the fourth pixel, and the fifthpixel as shown in FIG. 40B.

Note that in the case where blue light-emitting elements B1 and B2 eachhaving a different emission spectrum are disposed as the light-emittingelements which emit short-wavelength monochromatic light, the thicknessof the blue light-emitting elements B1 and B2 is varied likelight-emitting layers 4109A and 4109B shown in FIGS. 41A and 41B to varyemission spectrums. For example, in the case of a top emission structureas shown in FIG. 41A, the blue light-emitting layers 4109A and 4109Beach having a different emission spectrum are disposed as thelight-emitting elements which emit short-wavelength monochromatic light,and color conversion layers may be disposed above the first pixel, thesecond pixel, the fourth pixel, and the fifth pixel. Alternatively, inthe case of a bottom emission structure, the light-emitting layers 4109Aand 4109B of the blue light-emitting elements are disposed as shown inFIG. 41B, and the color conversion layers may be disposed below thefirst pixel, the second pixel, the fourth pixel, and the fifth pixel.Note that each structure of the display device in the invention shown inFIGS. 41A and 41B conforms to FIGS. 40A and 40B.

The color conversion method for converting a color of light emitted froma light-emitting element into a required color through a colorconversion layer is advantageous in that there is no need for separatelycoloring the light-emitting layers since a luminous color emitted fromthe light-emitting element is a monochromatic color. In addition,compared to a color filter method, the color conversion method ispreferable since it obtains desired light emission with the colorconversion layers using a process of absorption of light, excitation,and light emission.

Note that this embodiment can be freely combined with the otherembodiment modes or embodiments in this specification.

Embodiment Mode 4

In this embodiment mode, a configuration which is different from thearrangement of pixels in one picture element described in theaforementioned embodiment modes in FIG. 2 is described.

Note that description has been made of the configuration of the pixelportion of the invention where the picture element of the inventionincludes the first pixel, the second pixel, the third pixel, the fourthpixel, the fifth pixel, and the sixth pixel in FIG. 2. In addition, alight-emitting element is provided in each of the first pixel to thesixth pixel such that a light-emitting element R1, a light-emittingelement R2, a light-emitting element G1, a light-emitting element G2, alight-emitting element B1, and a light-emitting element B2 are connectedto the first pixel, the second pixel, the third pixel, the fourth pixel,the fifth pixel, and the sixth pixel, respectively.

In the disposition of pixels of a display device in this embodimentmode, a first pixel 1601, a second pixel 1602, a third pixel 1603, afourth pixel 1604, a fifth pixel 1605, and a sixth pixel 1606 which areincluded in a picture element 1600 as shown in FIG. 16 are arranged instripes.

Note that each of the first pixel 1601 to the sixth pixel 1606 isdisposed in a column direction in FIG. 16; however, a method fordisposing each pixel is not limited to this. For example, each pixel maybe disposed in a row direction, or the first pixel 1601 having thelight-emitting element R1 and the fifth pixel 1605 having thelight-emitting element G2 may be disposed to be adjacent to each other.In addition, the shape of each pixel is not limited to a rectangle asshown in FIG. 16, and for example, a square, other polygons, or a shapehaving a curvature may be employed.

Note also that the first pixel 1601 to the sixth pixel 1606 may bedisposed either at even intervals or not.

In addition, in FIG. 53A, the first pixel 1601, the second pixel 1602,and the third pixel 1603 are arranged in the first row while the fourthpixel 1604, the fifth pixel 1605, and the sixth pixel 1606 are arrangedin the next row, and the row of the first pixel 1601, the second pixel1602, and the third pixel 1603, and the row of the fourth pixel 1604,the fifth pixel 1605, and the sixth pixel 1606 may be shifted by onepixel. In this embodiment mode, the row of the first pixel 1601, thesecond pixel 1602, and the third pixel 1603, and the row of the fourthpixel 1604, the fifth pixel 1605, and the sixth pixel 1606 are shiftedby one pixel in the row direction; however, the number of pixels is notparticularly limited to one. For example, the row of the first pixel1601, the second pixel 1602, and the third pixel 1603, and the row ofthe fourth pixel 1604, the fifth pixel 1605, and the sixth pixel 1606may be shifted by half a pixel as shown in FIG. 53B. By employing anarrangement where pixels are shifted in this manner, smooth display canbe conducted particularly at the time of displaying a natural imagewhich is moving.

In the light-emitting element R1, the light-emitting element R2, thelight-emitting element G1, the light-emitting element G2, thelight-emitting element B1, and the light-emitting element B2, theluminous efficiency varies depending on a light-emitting element whichpresents each luminous color. Thus, in order to obtain light emissionwith desired luminance, relatively larger current is required to besupplied to a light-emitting element having low luminous efficiency.Further, human eyes have different sensitivity to each emissionwavelength, and in general, human eyes have higher sensitivity to agreen wavelength than a red wavelength or a blue wavelength.Accordingly, in order to make the blue light-emitting element or the redlight-emitting element emit light with the same luminous efficiency asthe green light-emitting element, luminance of the blue light-emittingelement or the red light-emitting element needs to be set relativelyhigher than the luminance of the green light-emitting element. However,when much current is supplied to the light-emitting element in order toobtain higher luminance, deterioration of the light-emitting element ispromoted and power consumption of the display device is increased. Inaddition, if a wavelength is shifted due to deterioration of thelight-emitting element, the color reproducibility of the display devicemay be decreased, which in turn decreases the image quality.

Therefore, a structure where area dimensions of the light-emittingelement R1, the light-emitting element R2, the light-emitting elementG1, the light-emitting element G2, the light-emitting element B1, andthe light-emitting element B2 are varied in advance may be employed. Forexample, a structure where area dimensions of the light-emittingelements R1, R2, B1, and B2 are doubled while area dimensions of thelight-emitting elements G1 and G2 are kept unchanged may be employed. Byemploying such a structure, variations of deterioration among thelight-emitting elements can be averaged, and thus, it is preferable.

Unlike the structure shown in FIG. 16, pixels of the display device inthis embodiment mode shown in FIG. 17 which include a first pixel 1701,a second pixel 1702, a third pixel 1703, a fourth pixel 1704, a fifthpixel 1705, and a sixth pixel 1706 in a picture element 1700 arearranged such that the first pixel 1701, the second pixel 1702, and thethird pixel 1703 are arranged in delta pattern, and the fourth pixel1704, the fifth pixel 1705, and the sixth pixel 1706 are also arrangedin delta pattern.

A structure where area dimensions of the first pixel 1701, the fourthpixel 1704, and the second pixel 1702 are varied from each other as wellas area dimensions of the fifth pixel 1705, the third pixel 1703, andthe sixth pixel 1706 are varied from each other is employed in FIG. 17;however, the invention is not limited to this. The area dimensions ofthe first pixel 1701, the fourth pixel 1704, and the second pixel 1702may be the same as well as the area dimensions of the fifth pixel 1705,the third pixel 1703, and the sixth pixel 1706 may be the same, or astructure where all of the first light-emitting element 1701 to thesixth pixel 1706 have different area dimensions from each other may beemployed. In addition, a structure of a picture element is notparticularly limited, and a structure where an image is formed by apicture element 1710 may be employed.

In addition, for example, the first pixel 1701 having the light-emittingelement R1 and the third pixel 1703 having the light-emitting element B1may be disposed to be adjacent to each other. In addition, the shape ofeach pixel is not limited to a rectangle as shown in FIG. 17, and forexample, a square, other polygons, or a shape having a curvature may beemployed. Note that the first pixel 1701 to the sixth pixel 1706 may bedisposed either at even intervals or not.

Further, in the display device of the invention, pixels are not limitedto the first pixel to the sixth pixel. A structure where a first pixel1801, a second pixel 1802, a third pixel 1803, a fourth pixel 1804, afifth pixel 1805, a sixth pixel 1806, a seventh pixel 1807, an eighthpixel 1808, and a ninth pixel 1809 are provided may be employed as shownin FIG. 18. Note that a structure where the seventh pixel 1807 has alight-emitting element R3, the eighth pixel 1808 has a light-emittingelement G3, and the ninth pixel 1809 has a light-emitting element B3 isemployed.

In FIG. 18, a structure where area dimensions of the first pixel 1801,the fourth pixel 1804, and the seventh pixel 1807 are varied from eachother, area dimensions of the second pixel 1802, the fifthlight-emitting element 1805, and the eighth pixel 1808 are varied fromeach other, and area dimensions of the third pixel 1803, the sixth pixel1806, and the ninth pixel 1809 are varied from each other is employed;however, the invention is not limited to this. The area dimensions ofthe first pixel 1801, the fourth pixel 1804, and the seventh pixel 1807may be the same, the area dimensions of the second pixel 1802, the fifthpixel 1805, and the eighth pixel 1808 may be the same, and the areadimensions of the third pixel 1803, the sixth pixel 1806, and the ninthpixel 1809 may be the same, or a structure where all of the first pixel1801 to the ninth pixel 1809 have different area dimensions from eachother may be employed.

In addition, in the display device of the invention, pixels are notlimited to the first pixel to the sixth pixel. A structure where a firstpixel 1901, a second pixel 1902, and a third pixel 1903, a fourth pixel1904, a fifth pixel 1905, a sixth pixel 1906, and a seventh pixel 1907are arranged may be employed as shown in FIG. 19A. Note that the seventhpixel 1907 has a structure where a white light-emitting element W isprovided.

Note that the light-emitting element W of the seventh pixel 1907 haschromaticity whose x-coordinate and y-coordinate in the CIE-XYchromaticity diagram are in the range of 0.30 to 0.40 and in the rangeof 0.30 to 0.40, respectively. More preferably, the light-emittingelement W of the seventh pixel 1907 has chromaticity whose x-coordinateand y-coordinate in the CIE-XY chromaticity diagram are in the range of0.30 to 0.35 and in the range of 0.30 to 0.35, respectively.

A structure where the area dimensions of the first pixel 1901 and thefourth pixel 1904 are the same, the area dimensions of the second pixel1902 and the fifth pixel 1905 are the same, and the area dimensions ofthe third pixel 1903 and the sixth pixel 1906 are the same is employedin FIG. 19A; however, the invention is not limited to this. A structurewhere area dimensions of the first pixel 1901 and the fourth pixel 1904vary from each other, area dimensions of the second pixel 1902 and thefifth pixel 1905 vary from each other, and area dimensions of the thirdpixel 1903 and the sixth pixel 1906 vary from each other may beemployed, or a structure where all of the pixel 1901 to the sixth pixel1906 have different area dimensions from each other may be employed.

A structure which is different from FIG. 19A is shown in FIG. 19B. Whatis different from FIG. 19A is the disposition of the first pixel 1901,the second pixel 1902, and the third pixel 1903, the fourth pixel 1904,the fifth pixel 1905, the sixth pixel 1906, and the seventh pixel 1907.Needless to say, disposition of each pixel is not particularly limitedto this. In addition, the shape of each pixel is not limited to arectangle as shown in FIG. 19A, and for example, a square, otherpolygons, or a shape having a curvature may be employed.

Note that by providing the light-emitting element W which emits whitelight in the seventh pixel, power consumption can be reduced since awhite color can be displayed by using light emission of only thelight-emitting element W compared to the case of displaying a whitecolor by using a color mixture of the light-emitting elements R1, R2,G1, G2, B1, and B2, and thus, it is preferable. In addition, when aneutral color is displayed by an additive color mixture using a whitecolor, more reduction in power consumption can be expected, and thus, itis preferable.

Note also that in the display device of the invention, a structure of apicture element where a light-emitting element W1 which emits whitelight is provided in the seventh pixel, and a light-emitting element W2which emits white light is provided in the eighth pixel may also beemployed. As well as the aforementioned light-emitting elements R1 andR2, light-emitting elements G1 and G2, and light-emitting elements B1and B2, emission spectrums of the light-emitting elements W1 and W2 arevaried from each other. Accordingly, a display device which displaysmore bright colors and has reduced power consumption can be provided.

Note that the light-emitting element W1 of the seventh pixel and thelight-emitting element W2 of the eighth pixel have chromaticity whosex-coordinate and y-coordinate in the CIE-XY chromaticity diagram are inthe range of 0.30 to 0.40 and in the range of 0.30 to 0.40,respectively. More preferably, the light-emitting element W1 of theseventh pixel and the light-emitting element W2 of the eighth pixel havechromaticity whose x-coordinate and y-coordinate in the CIE-XYchromaticity diagram are in the range of 0.30 to 0.35 and in the rangeof 0.30 to 0.35, respectively.

Note that this embodiment can be freely combined with the otherembodiment modes or embodiments in this specification.

Embodiment Mode 5

In this embodiment mode, configurations described in the aforementionedembodiment modes which are different from the pixel configuration andthe operation method shown in FIG. 4 and FIG. 5 are described.

According to the pixel configuration and the operation method shown inFIG. 4 and FIG. 5, there is an advantage that the length of sustain(light-emitting) periods can be freely set since address (writing)periods and the sustain (light-emitting) periods are completelyseparated; however, in the address (writing) periods, neither writingnor light emission is conducted in any other rows while writing isconducted in a certain row. That is, the duty ratio as a whole isdecreased.

Consequently, an operation where the address (writing) periods and thesustain (light-emitting) periods are not separated is described.

A pixel configuration for achieving the aforementioned operation isshown in FIG. 20. The pixel configuration shown in FIG. 20 includes afirst transistor 2001 for switching to control input of a video signal(also called a switching transistor), a second transistor 2002 fordriving to decide the state of lighting or non-lighting of alight-emitting element by the video signal (also called a drivingtransistor), a third transistor 2003 for erasing a gate-source voltageof the second transistor 2002 (also called an erasing transistor), alight-emitting element 2004, a storage capacitor 2005, a signal line2006, a first scan line 2007, a second scan line 2008, a power supplyline 2009, and an opposite electrode 2010. The storage capacitor 2005 isprovided so as to hold a gate-source voltage (gate voltage) of the firsttransistor 2001 and the second transistor 2002 more accurately; however,it is not necessarily required. Note that voltage means a potentialdifference from a ground unless otherwise specified. In addition, thelight-emitting element 2004 corresponds to the light-emitting elementsR1, R2, G1, G2, B1, and B2 in FIG. 2.

The first transistor 2001 is controlled by using the first scan line2007. When the first transistor 2001 is turned on, a video signal isinput from the signal line 2006 to the storage capacitor 2005. Then, inresponse to the video signal, the second transistor 2002 is turnedon/off, and a current flows from the power supply line 2009 to theopposite electrode 2010 through the light-emitting element 2004.

In the case of erasing a video signal, the second scan line 2008 isselected to turn on the third transistor 2003, and turn off the secondtransistor 2002. Then, a current does not flow from the power supplyline 2009 to the opposite electrode 2010 through the light-emittingelement 2004. Accordingly, a non-lighting period can be made so that thelength of a lighting period can be freely controlled.

Next, a timing chart in the case of conducting an operation of erasing asignal of a pixel is shown in FIG. 21. In this embodiment mode, a casewhere a 3-bit digital video signal is used in a digital time gray scalemethod similarly to FIG. 5 is described as an example. In the digitaltime gray scale method, one frame period 2101 is further divided into aplurality of sub frame periods. Here, since the video signal has 3 bits,the one frame period 2101 is divided into three sub frame periods, andwriting and displaying of each luminous color are conducted in each subframe period.

In FIG. 21, each sub frame period includes an address (writing) periodTa# (# is a natural number) and a sustain (light-emitting) period Ts#.In FIG. 21, in each sub frame period which is obtained by dividing theone frame period 2101, it can be seen that the address (writing) periodand the sustain (light-emitting) period are not separated. That is, uponcompletion of writing in an i-th row, light emission is startedimmediately in the i-th row. After that, while writing is conducted inan (i+1)-th row, the i-th row is already in the sustain (light-emitting)period. By employing such timing, the duty ratio can be increased.

However, in the case of the timing as shown in FIG. 21, a period when anaddress (writing) period in a certain sub frame period and an addressperiod in next sub frame period overlap with each other is generated ifthe sustain (light-emitting) period is shorter than the address(writing) period. Then, as shown in FIG. 20, by using the thirdtransistor, an erasing period Tr3 is forcibly provided from the time offinishing the sustain (light-emitting) period to the time of starting anext address (writing) period. By this erasing period Tr3, address(writing) periods in different sub frame periods can be prevented fromoverlapping with each other. Specifically, by using a second scan linedriver circuit for controlling the third transistor, selective pulsesfor erasing are sequentially output from a first row to turn on thethird transistor at desired timing. Note that the second scan linedriver circuit may have the same configuration as a first scan linedriver circuit which conducts normal writing. Accordingly, a period ofwriting signals for erasing (hereinafter, it is described as a resetperiod) Te3 has an equal length to the address (writing) period.

Note that although a case where the number of gray scale display bitsand the number of sub frames are the same is given as an example here,one frame may be further divided. In addition, gray scales can beexpressed even when the length ratio of the sustain (light-emitting)periods is not necessarily the power of two. By employing the pixelconfiguration shown in FIG. 20 in this manner, the length of thelighting period in each row can be easily controlled.

By employing the pixel configuration as shown in FIG. 20, many subframes can be arranged in one frame even if a signal writing operationis slow. In addition, in the case of conducting the erasing operation, adriving frequency of a source driver can also be reduced since there isno need for acquiring data for erasing like a video signal.

Alternatively, in the pixel configurations in FIG. 4 and FIG. 20, afield sequential method may be employed. In FIG. 22A, one frame perioddenoted by 2201 in the pixel configuration of FIG. 4 is divided into sixperiods denoted by 2202 to 2207, and writing and displaying of eachluminous color are conducted in each period. In addition, in FIG. 22B,one frame period denoted by 2201 in the pixel configuration of FIG. 20is divided into six periods shown with 2202 to 2207, and writing anddisplaying of each luminous color are conducted in each period.

Note that in FIGS. 22A and 22B, a case where a 3-bit digital videosignal is used in a digital time gray scale method is given as anexample. In the digital time gray scale method, the one frame period2201 is further divided into a plurality of sub frame periods. Here,since the video signal has 3 bits, the one frame period 2201 is dividedinto three sub frame periods.

Note also that in FIGS. 22A and 22B, one of the six periods denoted bythe first period 2202, the second period 2203, the third period 2204,the fourth period 2205, the fifth period 2206, and the sixth period 2207which correspond to the light-emitting elements R1, R2, G1, G2, B1, andB2, for example, the first period 2202 is described.

In the first period 2202, each sub frame period includes an address(writing) period Ta1 _(#) (# is a natural number) and a sustain(light-emitting) period Ts1 _(#). In addition, in the second period2203, each sub frame period includes an address (writing) period Ta2_(#) (# is a natural number) and a sustain (light-emitting) period Ts2_(#). Hereinafter, the third period 2204 to the sixth period 2207 aredescribed in the same manner.

In FIG. 22A, the length of the sustain (light-emitting) periods is Ts1₁: Ts1 ₂:Ts1 ₃=4:2:1, and 2³=8 gray scales are expressed by controllingthe state of lighting or non-lighting of the light-emitting element ineach sustain (light-emitting) period. That is, each sustain(light-emitting) period is set to have a power-of-two length of aprevious sustain (light-emitting) period such that Ts1 ₁:Ts1 ₂:Ts1₃=2^((n-1)):2^((n-2)): . . . :2¹:2⁰. For example, in the case where alight-emitting element emits light only in Ts1 ₃, and a light-emittingelement does not emit light in Ts1 ₁ and Ts1 ₂, light emission isobtained only in about 14% of all of the sustain (light-emitting)periods. That is, luminance of about 14% can be expressed. In the casewhere a light-emitting element emits light in Ts1 and Ts2, and alight-emitting element doe not emit light in Ts3, light emission isobtained in about 86% of all of the sustain (light-emitting) periods.That is, luminance of about 86% can be expressed.

As shown in FIG. 21, by conducting this operation repeatedly to expressluminous colors of the first to sixth pixels, that is, thelight-emitting elements R1, R2, G1, G2, B1, and B2 in FIG. 2, a viewercan view multicolor display by a residual image effect.

Although the third transistor 2003 is used in FIG. 20, another methodcan be employed as long as a current can be controlled not to besupplied to the light-emitting 2004 by forcibly making a non-lightingperiod. Accordingly, the non-lighting period may be made by disposing aswitch in somewhere on a path where a current flows from the powersupply line 2009 to the opposite electrode 2010 through thelight-emitting element 2004, and by controlling on/off of the switch.Alternatively, the gate-source voltage of the second transistor 2002 maybe controlled to forcibly turn off the second transistor 2002.

An example of a pixel configuration in the case of forcibly turning offthe second transistor 2002 is shown in FIG. 23. What is different fromFIG. 20 is that an erasing diode 2301 is connected between a gate of asecond transistor 2002 and a second scan line 2008.

In the case of erasing a video signal, the second scan line 2008 (here,it is set to be at a high potential) is selected to turn on the erasingdiode 2301, thereby a current flows from the second scan line 2008 tothe gate of the second transistor 2002. Accordingly, the secondtransistor 2002 is turned off. Then, a current does not flow from thepower supply line 2009 to the opposite electrode 2010 through thelight-emitting element 2004. Accordingly, a non-lighting period can bemade so that the length of a lighting period can be freely controlled.

In the case of holding the video signal, the second scan line 2008(here, it is set to be at a low potential) is not selected. Then, theerasing diode 2301 is turned off so that the gate potential of thesecond transistor 2002 is held.

Note that the erasing diode 2301 may be any element as long as it has arectifying property. Such an element may be a PN junction diode, a PINdiode, a Schottky diode, or a zener diode.

In addition, the erasing diode 2301 may be a diode-connected transistor(a transistor whose gate and drain are connected). A circuit diagram atthis case is shown in FIG. 24. As the erasing diode 2301, adiode-connected transistor 2401 is employed. Here, an n-channeltransistor is employed; however, the invention is not limited to this. Ap-channel transistor may also be employed.

Note that timing charts, pixel configurations, and driving methods shownin this embodiment mode are only exemplary, and the invention is notlimited to these. Various types of timing charts, pixel configurations,and driving methods can be applied.

Next, an operation region of a driving transistor in the case of adigital gray scale method is described. Note that FIG. 25 is acharacteristic diagram of an operation of the transistor where ahorizontal axis shows a gate-source voltage of the transistor while avertical axis shows a source-drain current of the transistor.

For example, in the case of operating the transistor in the saturationregion, there is an advantage that the value of a current which flows tothe light-emitting element does not change even if a current-voltagecharacteristic of the light-emitting element is deteriorated. Thus, thedisplay device is hardly influenced by ghosting. However, if a currentcharacteristic of the driving transistor varies, a current which flowsthereto also varies. Therefore, there is a case where display unevennessis generated.

On the other hand, in the case of operating the transistor in the linearregion, the value of a current which flows thereto is hardly influencedeven if the current characteristic of the driving transistor varies.Thus, display unevenness is hardly generated. In addition, powerconsumption can also be reduced since (the absolute value of) agate-source voltage of the driving transistor does not become too large.

Further, when (the absolute value of) a gate-source voltage of thedriving transistor is increased, a current which flows thereto is hardlyinfluenced even if the current characteristic of the driving transistorvaries. However, when the current-voltage characteristic of thelight-emitting element is deteriorated, there is a case where the valueof a current which flows thereto is changed. Therefore, the displaydevice is easily influenced by ghosting.

When the driving transistor operates in the saturation region in thismanner, the value of a current does not change even if thecharacteristics of the light-emitting element change. Accordingly, inthis case, the driving transistor can be regarded as operating as acurrent source. Therefore, this driving is called a constant currentdriving.

In addition, when the driving transistor operates in the linear region,the value of the current does not change even if the currentcharacteristic of the driving transistor varies. Accordingly, in thiscase, the driving transistor can be regarded as operating as a switch.Thus, it is regarded that a voltage of the power supply line is directlyapplied to the light-emitting element. Therefore, this driving is calleda constant voltage driving.

The invention can employ either the constant current driving or theconstant voltage driving. Accordingly, whether to employ the constantcurrent driving or the constant voltage driving may be changedappropriately in view of variations of the light-emitting element andthe transistor.

Note that this embodiment can be freely combined with the otherembodiment modes or embodiments in this specification.

Embodiment Mode 6

In this embodiment mode, description is made of another layout structureof each pixel and each wire in the invention.

FIG. 26 shows a layout diagram of the circuit diagram shown in FIG. 4.Note that the circuit diagram and the layout diagram are not limited toFIG. 4 and FIG. 26, respectively.

Switching transistors 2601A and 2601B, driving transistors 2602A and2602B, and electrodes of light-emitting elements R1 and R2 are disposed.Sources of the switching transistors 2601A and 2601B are connected to asignal line 2604, while drains thereof are connected to gates of thedriving transistors 2602A and 2602B, respectively. A gate of theswitching transistor 2601A is connected to a scan line 2605A, while agate of the switching transistor 2601B is connected to a scan line2605B. Sources of the driving transistors 2602A and 2602B are connectedto a power supply line 2606, while drains thereof are connected to theelectrodes of the light-emitting elements R1 and R2, respectively.Although a storage capacitor (not shown) is connected between the gateof either the driving transistor 2602A or 2602B and the power supplyline 2606, it is not necessarily required.

Note that the number of the signal lines 2604 may be more than onecorresponding to the driving transistors 2602A and 2602B.

The signal line 2604 and the power supply line 2606 are formed of asecond wire, while the scan lines 2605A and 2605B are formed of a firstwire.

FIG. 27 shows a top view of a pixel configuration corresponding to FIG.26. Reference numerals denoting the respective portions in FIG. 27correspond to those in FIG. 26.

In FIG. 27, in the case of a top-gate structure, films of a substrate, asemiconductor layer, a gate insulating film, a first wire, an interlayerinsulating film, and a second wire are formed in this order. In the caseof a bottom-gate structure, films of a substrate, a first wire, a gateinsulating film, a semiconductor layer, an interlayer insulating film,and a second wire are formed in this order. In addition, in FIG. 27,storage capacitors 2701A and 2701B are provided between the power supplyline and the first wires.

Although the description has been made of a double-gate structure whereeach of the switching transistors 2601A and 2601B is formed to have twochannel formation regions, a single-gate structure where one channelformation region is formed or a triple-gate structure where threechannel formation regions are formed may be used as well. Alternatively,a dual-gate structure where two gate electrodes are disposed above andbelow a channel formation region with gate insulating films sandwichedtherebetween, or other structures may be used.

In FIG. 27, when the distance between the light-emitting elements R1 andR2 in the same picture element is denoted by D1, the distance betweenthe light-emitting element R1 and a light-emitting element R2 of apicture element in another row is denoted by D2. According to a mode ofFIG. 27 in this embodiment mode, a structure where D1<D2 is provided,and thus the distance between the light-emitting elements R1 and R2 inthe same picture element can be shortened. In the invention, thelight-emitting elements R1 and R2 are arranged in parallel in the columndirection (the vertical direction in FIG. 26), and no scan line isdisposed between the light-emitting elements R1 and R2 as shown in FIG.27, which is preferable in that a color mixture of the light-emittingelements R1 and R2 can be more visible. Needless to say, light-emittingelements G1 and G2, and light-emitting elements B1 and B2 preferablyhave a similar structure to the light-emitting elements R1 and R2 inorder to make a color mixture more visible. In addition, in the case ofarranging the light-emitting elements R1 and R2 in parallel in the rowdirection (the horizontal direction in FIG. 26), it is preferable not todispose a power supply line between the light-emitting elements R1 andR2, which allows the light-emitting elements R1 and R2 to be locatedmore closer to each other.

In the pixel of FIG. 26, the scan line 2605B can be replaced by a scanline 2605A of a pixel in another row. That is, the scan line 2605B ofthe display device shown in FIG. 26 can be omitted. FIG. 28 shows anexemplary configuration in the case where the scan line 2605B in thepixel of FIG. 26 is omitted and replaced by the scan line 2605A of apixel in another row.

The configurations of the display device shown in FIGS. 26 and 28 areonly illustrative, and thus the invention is not limited to these. Forexample, the power supply line is not necessarily required to bedisposed in parallel with the signal line, and may be provided inparallel with the scan line, or each power supply line may be providedin grid patterns. That is, the power supply line in the pixel in FIG. 26may be provided in parallel with the scan line as shown in FIG. 29.

As described above, wires provided around a pixel of the display deviceof the invention can have various structures, and thus the invention isnot limited to the structures described in this specification.

Note that this embodiment mode can be freely combined with the otherembodiment modes or embodiments in this specification.

Embodiment Mode 7

In this embodiment mode, description is made of a structure of a displaypanel having a pixel configuration shown in the aforementionedembodiment, with reference to FIGS. 30A and 30B.

Note that FIG. 30A is a top view showing a display panel, and FIG. 30Bis a cross-sectional view taken along a line A-A′ of FIG. 30A. Thedisplay panel includes a signal line driver circuit 3001, a pixelportion 3002, a first scan line driver circuit 3003, and a second scanline driver circuit 3006, which are shown by dotted lines. The displaypanel also includes a sealing substrate 3004 and a sealant 3005, and theinner side of the sealant 3005 is a space 3007.

Note that a wire 3008 is a wire for transmitting signals to be inputinto the first scan line driver circuit 3003, the second scan linedriver circuit 3006, and the signal line driver circuit 3001, andreceives video signals, clock signals, start signals, and the like froman FPC 3009 (Flexible Printed Circuit) which serves as an external inputterminal. An IC chip 3019 (a semiconductor chip incorporating a memorycircuit, a buffer circuit, and the like) is mounted on a connectingportion between the FPC 3009 and the display panel by COG (Chip OnGlass) or the like. Although only an FPC is shown in the drawing, aprinted wiring board (PWB) may be attached to the FPC. A display devicein this specification includes not only a main body of a display panel,but includes a display panel in the condition that an FPC or a PWB isattached. Further, it also includes a display panel on which an IC chipand the like are mounted.

Next, a cross-sectional structure is described with reference to FIG.30B. Although the pixel portion 3002 and its peripheral driver circuits(the first scan line driver circuit 3003, the second scan line drivercircuit 3006, and the signal line driver circuit 3001) are actuallyformed over the substrate 3010, only the signal line driver circuit 3001and the pixel portion 3002 are shown herein.

The signal line driver circuit 3001 is constructed from transistors ofsingle conductivity type, such as an n-channel TFT 3020 and an n-channelTFT 3021. Note that in the case of constructing pixels by usingtransistors of single conductivity type, given that a peripheral drivercircuit is constructed by using only n-channel transistors, a singleconductivity type display panel can be manufactured. Needless to say,not only transistors of single conductivity type, but a CMOS circuitconstructed from an n-channel transistor and a p-channel transistor maybe used. In addition, although this embodiment mode shows a displaypanel where a pixel portion and peripheral driver circuits are formedover the same substrate, the invention is not necessarily limited tothis and a part or all of the peripheral driver circuits may be formedin an IC chip so that it is mounted on the display panel by COG or thelike. In such a case, the driver circuit is not required to be formedfrom transistors of single conductivity type, and thus it may be formedby combining an n-channel transistor and a p-channel transistor.

The pixel portion 3002 includes a TFT 3011 and a TFT 3012. Note that asource electrode of the TFT 3012 is connected to a first electrode 3013(pixel electrode). In addition, an insulator 3014 is formed covering theedge of the first electrode 3013. Here, the insulator 3014 is formed byusing a positive photosensitive acrylic resin film.

In order to obtain an excellent coverage, a top edge or a bottom edge ofthe insulator 3014 is formed to have a curved surface with a curvature.For example, in the case of using positive photosensitive acrylic as amaterial of the insulator 3014, it is preferable to form only the topedge of the insulator 3014 to have a curvature radius (0.2 to 3 μm).Alternatively, the insulator 3014 can be formed by using a negativephotoresist which becomes insoluble in etchant by light or a positivephotoresist which becomes soluble in etchant by light.

A light-emitting layer 3016 and a second electrode 3017 (oppositeelectrode) are formed over the first electrode 3013. Here, as a materialused for the first electrode 3013 functioning as an anode, a materialwith a high work function is desirably used. For example, the firstelectrode 3103 can be formed with a single film such as an ITO (IndiumTin Oxide) film, an indium zinc oxide (IZO) film, a titanium nitridefilm, a chromium film, a tungsten film, a Zn film, or a Pt film, stackedlayers of a titanium nitride film and a film containing aluminum as itsmain component, or a three-layer structure of a titanium nitride film, afilm containing aluminum as its main component, and a titanium nitridefilm, or the like. When the first electrode 3103 is formed to have astacked structure, low resistance as a wire can be obtained, anexcellent ohmic contact can be formed, and further a function as ananode can be obtained.

The light-emitting layer 3016 is formed by a vapor deposition methodusing a vapor-deposition mask or an ink-jet method. A part of thelight-emitting layer 3016 is formed by using a metal complex of theGroup 4 in the periodic table, which may be combined with either a lowmolecular material or a high molecular material. In general, thematerial used for the light-emitting layer is often an organic compoundwith a single layer or stacked layers; however, a structure where a filmmade of an organic compound partially contains an inorganic compound maybe used as well. Further, known triplet materials can be used.

As a material used for the second electrode 3017 formed over thelight-emitting layer 3016, a material with a low work function (e.g.,Al, Ag, Li, or Ca; or alloys of these such as MgAg, Men, AlLi, CaF₂, orcalcium nitride) may be used. Note that in the case where lightgenerated in the light-emitting layer 3016 is made travel through thesecond electrode 3017, the second electrode 3017 (cathode) is preferablyformed of stacked layers of a thin metal film and a light-transmissiveconductive film (e.g., ITO (an alloy of indium oxide and tin oxide), analloy of indium oxide and zinc oxide (In₂O₃—ZnO), zinc oxide (ZnO), orthe like).

Further, by attaching the sealing substrate 3004 to the substrate 3010with the sealant 3005, a structure where a light-emitting element 3018is provided in the space 3007 surrounded by the substrate 3010, thesealing substrate 3004, and the sealant 3005 is formed. Note that thespace 3007 may be filled with an inert gas (e.g., nitrogen, argon, orthe like) or filled with the sealant 3005.

Note that the sealant 3005 is preferably formed with an epoxy resin. Inaddition, such a material desirably transmits as little moisture andoxygen as possible. As a material used for the sealing substrate 3004, aplastic substrate made of FRP (Fiberglass-Reinforced Plastics), PVF(Polyvinyl Fluoride), mylar, polyester, acrylic, or the like can be usedin addition to a glass substrate or a quartz substrate.

In this manner, a display panel having a pixel configuration of theinvention can be obtained. Note that the aforementioned configuration isonly illustrative, and thus the structure of the display panel of theinvention is not limited to this.

By forming the signal line driver circuit 3001, the pixel portion 3002,the first scan line driver circuit 3003, and the second scan line drivercircuit 3006 over the same substrate as shown in FIG. 30, cost reductionof the display device can be achieved. In addition, in this case, whenthe signal line driver circuit 3001, the pixel portion 3002, the firstscan line driver circuit 3003, and the second scan line driver circuit3006 are formed by using transistors of single conductivity type, themanufacturing process can be simplified, which leads to a further costreduction.

Note that a structure of a display panel is not limited to the structurewhere the signal line driver circuit 3001, the pixel portion 3002, thefirst scan line driver circuit 3003, and the second scan line drivercircuit 3006 are formed over the same substrate as shown in FIG. 30A,and a structure where a signal line driver circuit 3101 shown in FIG. 31which corresponds to the signal line driver circuit 3001 is formed in anIC chip so that it is mounted on the display panel by COG or the likemay be used. Note that a substrate 3100, a pixel portion 3102, a firstscan line driver circuit 3103, a second scan line driver circuit 3104,an FPC 3105, an IC chip 3106, an IC chip 3107, a sealing substrate 3108,and a sealant 3109 in FIG. 31A correspond to the substrate 3010, thepixel portion 3002, the first scan line driver circuit 3003, the secondscan line driver circuit 3006, the FPC 3009, the IC chip 3019, thesealing substrate 3004, and the sealant 3005 in FIG. 30A, respectively.

That is, only a signal line driver circuit which is required to performa high-speed operation is formed in an IC chip using a CMOS or the likein order to achieve low power consumption. In addition, by forming an ICchip using a semiconductor chip such as a silicon wafer, a higher-speedoperation and lower power consumption can be achieved.

By forming the first scan line driver circuit 3103 and the second scanline driver circuit 3104 over the same substrate as the pixel portion3102, cost reduction can be achieved. Further, by forming the first scanline driver circuit 3103, the second scan line driver circuit 3104, andthe pixel portion 3102 using transistors of single conductivity type,further cost reduction can be achieved. As a configuration of pixelsincluded in the pixel portion 3102, the pixels shown in Embodiment Modes1, 2, 3, and 4 can be used.

In this manner, cost reduction of a high-definition display device canbe achieved. In addition, by mounting an IC chip which incorporates afunctional circuit (e.g., a memory or a buffer) on a connecting portionbetween the FPC 3105 and the substrate 3100, the substrate area can beeffectively utilized.

Alternatively, after forming a signal line driver circuit 3111, a firstscan line driver circuit 3114, and a second scan line driver circuit3113 in FIG. 31B, which correspond to the signal line driver circuit3001, the first scan line driver circuit 3003, and the second scan linedriver circuit 3006 in FIG. 30A, respectively, in IC chips, the IC chipsmay be mounted on the display panel by COG or the like. In this case,power consumption of a high-definition display device can be furtherreduced. Therefore, in order to obtain a display device with lower powerconsumption, polysilicon is desirably used for semiconductor layers ofthe transistors which are used in the pixel portion. A substrate 3110, apixel portion 3112, an FPC 3115, an IC chip 3116, an IC chip 3117, asealing substrate 3118, and a sealant 3119 in FIG. 31B correspond to thesubstrate 3010, the pixel portion 3002, the FPC 3009, the IC chip 3019,the sealing substrate 3004, and the sealant 3005 in FIG. 30A,respectively.

In addition, by using amorphous silicon for semiconductor layers of thetransistors in the pixel portion 3112, further cost reduction can beachieved. Further, a large display panel can be manufactured.

The second scan line driver circuit, the first scan line driver circuit,and the signal line driver circuit are not required to be provided inthe row direction and the column direction of the pixels. For example,as shown in FIG. 32A, a peripheral driver circuit 3201 formed in an ICchip may incorporate the functions of the first scan line driver circuit3114, the second scan line driver circuit 3113, and the signal linedriver circuit 3111 shown in FIG. 31B. Note that a substrate 3200, apixel portion 3202, an FPC 3204, an IC chip 3205, an IC chip 3206, asealing substrate 3207, and a sealant 3208 in FIG. 32A correspond to thesubstrate 3010, the pixel portion 3002, the FPC 3009, the IC chip 3019,the sealing substrate 3004, and the sealant 3005 in FIG. 30A,respectively.

FIG. 32B shows a schematic view for illustrating a connection of wiresin the display device of FIG. 32A. The display device includes asubstrate 3210, a peripheral driver circuit 3211, a pixel portion 3212,an FPC 3213, and an FPC 3214. External signals and power supplypotentials are input into the peripheral driver circuit 3211 from theFPC 3213. Output from the peripheral driver circuit 3211 is input intowires in the row and column directions which are connected to the pixelsincluded in the pixel portion 3212.

As described above, a display panel of the display device of theinvention can have various structures, and thus is not limited to thestructures described in this specification.

Note that this embodiment mode can be freely combined with the otherembodiment modes or embodiments in this specification.

Embodiment Mode 8

In this embodiment mode, description is made of another structure ofeach pixel and a cross-sectional structure of a transistor in theinvention.

FIGS. 44A to 44C show exemplary circuit diagrams in this embodimentmode. Note that the circuit diagram is not limited to the ones shown inFIGS. 44A to 44C. The circuit diagrams illustrated in FIGS. 44A to 44Care the circuit diagrams using only n-channel transistors. Byconstructing a circuit which constitutes a pixel by using only n-channeltransistors, a display device which can be formed through, a simpleprocess and can accommodate a large substrate can be provided.Hereinafter, specific examples of them are described.

FIG. 44A shows a circuit configuration. In a pixel, a first transistor4401, a second transistor 4402, and a light-emitting element 4406 aredisposed. A signal line 4403 to which video signals are input isconnected to a gate of the second transistor 4402 through the firsttransistor 4401. A gate of the first transistor 4401 is connected to ascan line 4407. The second transistor 4402 and a light-emitting element4406 are connected between a first power supply line 4404 and a secondpower supply line 4405. Current flows from the first power supply line4404 to the second power supply line 4405. The light-emitting element4406 emits light in accordance with the amount of current flowingthereto.

A storage capacitor may be provided in order to hold video signals inputto the gate of the second transistor 4402. In that case, the storagecapacitor may be provided either between the gate of the secondtransistor 4402 and a drain of the second transistor 4402, or betweenthe gate of the second transistor 4402 and a source of the secondtransistor 4402. Alternatively, the storage capacitor may be providedbetween the gate of the second transistor 4402 and another wire (adedicated wire, a scan line of a pixel in the preceding row, or thelike). As a further alternative, the storage capacitor may be replacedby the gate capacitance of the second transistor 4402. Note that thesecond transistor 4402 and the first transistor 4401 are n-channeltransistors.

FIG. 44B shows another circuit configuration of this embodiment mode. Ina pixel, a first transistor 6001, a second transistor 6002, a thirdtransistor 6009 (also called a storage transistor), a storage capacitor6010, and a light-emitting element 6006 are disposed. A signal line 6003to which video signals are input is connected to a source of the secondtransistor 6002 through the first transistor 6001. A gate of the firsttransistor 6001 is connected to a scan line 6007. The second transistor6002 and a light-emitting element 6006 are connected between a firstpower supply line 6004 and a second power supply line 6005. Currentflows from the first power supply line 6004 to the second power supplyline 6005. The light-emitting element 6006 emits light in accordancewith the amount of current flowing thereto. The storage capacitor 6010is disposed between a gate and the source of the second transistor 6002,and the third transistor 6009 is connected between the gate and a drainof the second transistor 6002. A gate of the third transistor 6009 isconnected to the scan line 6007.

A current source circuit 6008 is disposed in a signal line drivercircuit. The current source circuit 6008 supplies a current to a pixelin accordance with the size of a video signal. A video signal which issupplied to the source signal line 6003 upon selection of the scan line6007 is input to the second transistor 6002. At this time, no currentflows into the light-emitting element 6006 because of the potentialrelationship between the first power supply line 6004 and the secondpower supply line 6005, since the potential of the first power supplyline 6004 is changed. Then, a gate-source voltage of the secondtransistor 6002 with a required level is held in the storage capacitor6010 in accordance with the size of a video signal. After that, the scanline 6007 is turned into a non-selection state, so that the chargesaccumulated in the storage capacitor 6010 are held. Accordingly, thegate-source voltage of the second transistor 6002 does not change evenwhen the drain potential or the source potential of the secondtransistor 6002 changes. Then, the potential of the first power supplyline 6004 returns to a former level, so that a current with an amountcorresponding to a video signal flows through the second transistor 6002to be delivered to the light-emitting element 6006.

FIG. 44C shows another circuit configuration of this embodiment mode. Ina pixel, a first transistor 7001, a second transistor 7002, a thirdtransistor 7009, a storage capacitor 7010, and a light-emitting element7006 are disposed. A signal line 7003 to which video signals are inputis connected to a gate of the second transistor 7002 through the firsttransistor 7001. A gate of the first transistor 7001 is connected to afirst scan line 7007. The second transistor 7002 and a light-emittingelement 7006 are connected between a first power supply line 7004 and asecond power supply line 7005. Current flows from the first power supplyline 7004 to the second power supply line 7005. The light-emittingelement 7006 emits light in accordance with the amount of currentflowing thereto. The storage capacitor 7010 is disposed between the gateand a source of the second transistor 7002, and the third transistor7009 is connected between the gate and a drain of the second transistor7002. A gate of the third transistor 7009 is connected to a second scanline 7016.

In the circuit configuration shown in FIG. 44C, the third transistor7009 is turned on in response to a signal input from the second scanline 7016. Then, a gate-source voltage of the second transistor 7002which has a level equal to the threshold voltage of the secondtransistor 7002 is held in the storage capacitor 7010. Therefore,variations in the threshold voltage of each driving voltage can becorrected in advance. Note that a voltage higher than the thresholdvoltage of the transistor may be held in the storage capacitor 7010 inadvance by increasing the potential of the second power supply line 7005only for an instant.

Then, a video signal supplied to the signal line 7003 is input to thegate of the second transistor 7002. Then, a current corresponding to thesize of a video signal flows through the second transistor 7002 to bedelivered to the light-emitting element 7006.

In FIGS. 44A to 44C, the second transistor may be operated only in thesaturation region, operated both in the saturation region and the linearregion, or operated only in the liner region.

In the case where the second transistor is operated only in the linearregion, it roughly operates as a switch. Therefore, fluctuations ofcharacteristics of the second transistor due to the deterioration,temperature, and the like will have few effects on the switchingoperation. In the case where the second transistor is operated only inthe linear region, whether to flow a current into the light-emittingelement 7006 or not is often controlled digitally. In that case, a timegray-scale method, an area gray-scale method, and the like may becombined in order to achieve multi-gray scales.

Next, a case is described where an amorphous silicon (a-Si:H) film isused for a semiconductor layer of a transistor in the circuitconfigurations shown in FIGS. 44A to 44C. FIGS. 42A and 42B showexamples of a top-gate transistor, while FIGS. 43A and 43B and FIGS. 49Aand 49B show examples of a bottom-gate transistor.

FIG. 42A shows a cross section of a staggered transistor which usesamorphous silicon as a semiconductor layer. As shown in FIG. 42A, a basefilm 7602 is formed over a substrate 7601. Further, a pixel electrode7603 is formed over the base film 7602. In addition, a first electrode7604 is formed with the same material and in the same layer as the pixelelectrode 7603.

As a substrate, any of a glass substrate, a quartz substrate, a ceramicsubstrate, a plastic substrate, and the like can be used. In addition,as the base film 7602, a single layer of aluminum nitride (AlN), siliconoxide (SiO₂), silicon oxynitride (SiO_(x)N_(y)), or the like, or stackedlayers thereof can be used.

Wires 7605 and 7606 are formed over the base film 7602, and the edge ofthe pixel electrode 7603 is covered with the wire 7605. N-typesemiconductor layers 7607 and 7608 each having n-type conductivity areformed over the wires 7605 and 7606, respectively. A semiconductor layer7609 is formed between the wires 7605 and 7606, and over the base film7602. A part of the semiconductor layer 7609 is extended to partiallycover the n-type semiconductor layers 7607 and 7608. Note that thesemiconductor layer 7609 is formed of a non-crystalline semiconductorfilm which is made of amorphous silicon (a-Si:H), a microcrystallinesemiconductor (μ-Si:H), or the like. A gate insulating film 7610 isformed over the semiconductor layer 7609. In addition, an insulatingfilm 7611 which is formed with the same material and in the same layeras the gate insulating film 7610 is formed over the first electrode7604. Note that the gate insulating film 7610 is formed of a siliconoxide film, a silicon nitride film, or the like.

A gate electrode 7612 is formed over the gate insulating film 7610. Inaddition, a second electrode 7613 which is formed with the same materialand in the same layer as the gate electrode 7612 is formed over thefirst electrode 7604 with the insulating film 7611 sandwichedtherebetween. By sandwiching the insulating film 7611 between the firstelectrode 7604 and the second electrode 7613, a storage capacitor 7619is formed. An interlayer insulating film 7614 is formed covering theedge of the pixel electrode 7603, a driving transistor 7618, and thestorage capacitor 7619.

A light-emitting layer 7615 and an opposite electrode 7616 are formedover the interlayer insulating film 7614 and the pixel electrode 7603positioned in an opening of the interlayer insulating film 7614. Thus, alight-emitting element 7617 is formed in a region where thelight-emitting layer 7615 is sandwiched between the pixel electrode 7603and the opposite electrode 7616.

The first electrode 7604 shown in FIG. 42A may be replaced by a firstelectrode 7620 as shown in FIG. 42B. The first electrode 7620 is formedwith the same material and in the same layer as the wires 7605 and 7606.

FIGS. 43A and 43B show partial cross sections of a display panel havinga bottom-gate transistor which uses amorphous silicon as a semiconductorlayer.

A base film 7702 is formed over a substrate 7701. Further, a gateelectrode 7703 is formed over the base film 7702. In addition, a firstelectrode 7704 is formed with the same material and in the same layer asthe gate electrode 7703. As a material of the gate electrode 7703,polysilicon doped with phosphorus can be used Not only polycrystallinesilicon, but also silicide which is a compound of a metal and siliconmay be used as well.

In addition, a gate insulating film 7705 is formed covering the gateelectrode 7703 and the first electrode 7704. The gate insulating film7705 is formed of a silicon oxide film, a silicon nitride film, or thelike.

A semiconductor layer 7706 is formed over the gate insulating film 7705.In addition, a semiconductor layer 7707 is formed with the same materialand in the same layer as the semiconductor layer 7706.

As a substrate, any of a glass substrate, a quartz substrate, a ceramicsubstrate, a plastic substrate, and the like can be used. In addition,as the base film 7702, a single layer of aluminum nitride (AlN), siliconoxide (SiO₂), silicon oxynitride (SiO_(x)N_(y)), or the like, or stackedlayers thereof can be used.

N-type semiconductor layers 7708 and 7709 each having n-typeconductivity are formed over the semiconductor layer 7706, while ann-type semiconductor layer 7710 is formed over the semiconductor layer7707.

Wires 7711, 7712, and 7713 are formed over the n-type semiconductorlayers 7708, 7709, and 7710, respectively, and the conductive layer 7713which is formed with the same material and in the same layer as thewires 7711 and 7712 is formed over the n-type semiconductor layer 7710.

A second electrode is formed of the semiconductor layer 7707, the n-typesemiconductor layer 7710, and the conductive layer 7713. Note that astorage capacitor 7720 is formed in a region where the gate insulatingfilm 7705 is sandwiched between the second electrode and the firstelectrode 7704.

In addition, a part of the wire 7711 is extended, and a pixel electrode7714 is formed in contact with the top surface of the extended portionof the wire 7711.

An insulator 7715 is formed covering the edge of the pixel electrode7714, a driving transistor 7719, and the storage capacitor 7720.

A light-emitting layer 7716 and an opposite electrode 7717 are formedover the pixel electrode 7714 and the insulator 7715, and alight-emitting element 7718 is formed in a region where thelight-emitting layer 7716 is sandwiched between the pixel electrode 7714and the opposite electrode 7717.

The semiconductor layer 7707 and the n-type semiconductor 7710 whichpartially function as a second electrode of the storage capacitor arenot necessarily provided. That is, only the conductive layer 7713 may beused as the second electrode, so that the storage capacitor has astructure where a gate insulating film is sandwiched between the firstelectrode 7704 and the conductive layer 7713.

Note that by forming the pixel electrode 7714 before forming the wire7711 shown in FIG. 43A, a storage capacitor 7720 as shown in FIG. 43Bcan be formed, which has a structure where the gate insulating film 7705is sandwiched between the first electrode 7704 and a second electrode7721 which is formed of the same material and in the same layer as thepixel electrode 7714.

Although FIGS. 43A and 43B show inversely staggered transistors with achannel-etched structure, a transistor with a channel-protectivestructure may be employed as well. Next, description is made of a caseof a transistor with a channel-protective structure, with reference toFIGS. 49A and 49B.

A transistor with a channel-protective stricture shown in FIG. 49A isdifferent from the driving transistor 7719 with a channel-etchedstructure shown in FIG. 43A in that an insulator 7801 serving as anetching mask is provided over a channel formation region in thesemiconductor layer 7706. Portions common to FIGS. 49A and 43A aredenoted by common reference numerals.

Similarly, a transistor with a channel-protective structure shown inFIG. 49B is different from the driving transistor 7719 with achannel-etched structure shown in FIG. 43B in that an insulator 7802serving as an etching mask is provided over a channel formation regionin the semiconductor layer 7706. Portions common to FIGS. 49B and 43Bare denoted by common reference numerals.

By using an amorphous semiconductor film for a semiconductor layer(e.g., a channel formation region, a source region, or a drain region)of a transistor which partially constitutes a pixel of the invention,manufacturing cost can be reduced. For example, an amorphoussemiconductor film can be applied by using the pixel configurationsshown in FIGS. 44A to 44C.

Note that this embodiment mode can be freely combined with the otherembodiment modes or embodiments in this specification.

Embodiment Mode 9

In this embodiment mode, description is made of a structure of a passivedisplay panel which can be applied to the invention.

FIG. 47A is a top view of a pixel portion before being sealed. FIG. 47Bis a cross-sectional view taken along a chain dash line A-A′ in FIG.47A, and FIG. 47C is a cross-sectional view taken along a chain dashline B-B′ in FIG. 47A.

A plurality of first electrodes 2113 are disposed in stripe patterns ateven intervals over a substrate 2110. A partition wall 2114 havingopenings corresponding to the respective pixels is provided over thefirst electrode 2113. The partition wall 2114 having openings is formedof a light-shielding material (black pigment, a photosensitive ornon-photosensitive organic material in which carbon black is dispersed(e.g., polyimide, acrylic, polyamide, polyimide amide, resist, orbenzocyclobutene), or an SOG film (e.g., a SiO_(x) film containing analkyl group)). For example, a material such as COLOR MOSAIC® CK(registered trademark of FUJIFILM OLIN Co., Ltd) is used for thepartition wall 2114 having openings. The partition wall 2114 havingopenings functions as a black matrix (BM). Note that the openingcorresponding to each pixel functions as a light-emitting region 2121.

Over the partition wall 2114 having openings, a plurality of parallelpartition walls 2122 with inversely tapered shapes are provided,crossing the first electrodes 2113. The inversely tapered partitionwalls 2122 are formed by photolithography using a positivephotosensitive resin by which unexposed regions remain as patterns, sothat lower portions of the patterns are etched more by controlling thequantity of exposure light or the developing time. The inversely taperedpartition walls 2122 may also be formed with the aforementionedlight-shielding material so as to further improve the contrast.

FIG. 48 shows a perspective view immediately after forming the pluralityof parallel partition walls 2122 with inversely tapered shapes. Notethat common portions to FIGS. 48 and 47A to 47C are denoted by commonreference numerals.

The height of the inversely tapered partition walls 2122 is set to behigher than the thickness of a film containing an organic compound and aconductive film. When a film containing an organic compound and aconductive film are stacked over the first substrate having thestructure shown in FIG. 48, they are separated into a plurality ofregions which are electrically insulated from each other, therebylight-emitting layers and second electrodes 2116 are formed. The secondelectrodes 2116 are parallel striped electrodes which extend in thedirection of crossing the first electrodes 2113. Note that the filmcontaining an organic compound and the conductive film are also formedover the inversely tapered partition walls 2122; however, they areseparated from light-emitting layers 21158, 21150 and 2115B, and thesecond electrodes 2116.

Note that in this embodiment mode, a first light-emitting element R1 ofthe invention corresponds to the light-emitting layer 2115R; a thirdlight-emitting element G1 of the invention corresponds to thelight-emitting layer 2115G; and a fifth light-emitting element B1 of theinvention corresponds to the light-emitting layer 2115B. Note also thatin this embodiment mode, the second light-emitting element R2 of theinvention corresponds to a region below the light-emitting layer 2115Rin FIG. 47A; the fourth light-emitting element G2 of the inventioncorresponds to a region below the light-emitting layer 2115G in FIG.47A; and the sixth light-emitting element B2 of the inventioncorresponds to a region below the light-emitting layer 2115B in FIG.47A. As a method of varying the emission spectrums of the light-emittingelements R1 and R2 from each other; varying the emission spectrums ofthe light-emitting elements G1 and G2 from each other; and varying theemission spectrums of the light-emitting elements B1 and B2 from eachother, either a material or thickness of the respective light-emittingelements may be varied, or color filters or color conversion layershaving different transmission properties may be used. In this embodimentmode, description is made of the light-emitting layers 2115R, 2115G, and2115B, and not the whole pixels will be described.

An example shown herein is a case where the light-emitting layers 2115R,2115G and 2115B are selectively formed to form a light-emitting devicecapable of a full color display with which three kinds of light emission(R, and B) are obtained. The light-emitting layers 2115R, 2115G and2115B are formed in stripe patterns which are parallel with each other.

Sealing of the light-emitting elements is carried out by attaching asecond substrate to the first substrate with a sealant. A protectivefilm for covering the second electrodes 2116 may also be formed ifnecessary. Note that the second substrate is preferably a substratehaving a high bather property against moisture. In addition, a dryingagent may be disposed in a region surrounded by a sealant if necessary.

FIG. 50 shows a top view of a light-emitting module on which an FPC andthe like are mounted after sealing.

Note that a light-emitting device in this specification means an imagedisplay device, a light-emitting device, or a light source (including anilluminating device). In addition, a light-emitting device includes amodule to which a connector such as an FPC (Flexible Printed Circuit), aTAB (Tape Automated Bonding) tape, or a TCP (Tape Carrier Package) isattached, a module where an end of the TAB tape or the TCP is providedwith a printed wiring board, or a module where an IC (IntegratedCircuit) is directly mounted on light-emitting elements by COG (Chip OnGlass).

A first substrate 5001 and a second substrate 5010 are attached with asealant 5011 so as to face each other. The sealant 5011 may be aphoto-curing resin, and is preferably a material with few degasificationand a low hygroscopic property. In addition, in order to keep a constantgap between the substrates, fillers (spacers in stick or fiber forms) orspherical spacers may be added to the sealant 5011. Note that the secondsubstrate 5010 is preferably formed of a material having the samethermal expansion coefficient as the first substrate 5001, and glass(including quartz glass) or plastic can be used.

In a pixel portion where an image display is performed as shown in FIG.50, column signal lines and row signal lines cross at right angles witheach other.

The first electrode 2113 in FIGS. 47A to 47C corresponds to a columnsignal line 5002 in FIG. 5; the second electrode 2116 in FIGS. 47A to47C corresponds to a row signal line 5003; and the inversely taperedpartition wall 2122 in FIG. 47C corresponds to a partition wall 5004. Alight-emitting layer is sandwiched between the column signal line 5002and the row signal line 5003, and one intersection 5005 corresponds toone pixel.

Note that the row signal line 5003 is electrically connected on its endto a connecting wire 5008, and the connecting wire 5008 is connected toan FPC 5009 b through an input terminal 5007. The column signal line5002 is connected to an FPC 5009 a through an input terminal 5006.

In addition, an optical film such as a polarizing plate, a circularlypolarizing light plate (including an elliptically polarizing plate), aretardation plate (a λ/4 plate or a λ/2 plate), or a color filter may beprovided as appropriate on the light-emission surface. In addition, thepolarizing plate or the circularly polarizing plate may be provided withan anti-reflection film. For example, anti-glare treatment may beapplied to the polarizing plate or the circularly polarizing plate byforming irregularities on the surface in order to diffuse reflectedlight and reduce glare. In addition, anti-reflection treatment bythermal treatment may be applied to the polarizing plate or thecircularly polarizing plate. After that, hard-coat treatment may befurther applied for protection against external shocks. However, when apolarizing plate or a circularly polarizing plate is used, the lightextraction efficiency is decreased. In addition, the polarizing plate orthe circularly polarizing plate itself is expensive and easilydeteriorates.

In this embodiment mode, stray light from the light-emitting elements isabsorbed or shielded by providing black partition walls (also calledbanks or partitions) which serve as a black matrix (BM) between pixelson the side of the substrate where light-emitting elements are provided,thereby the contrast of a display can be improved.

Note that this embodiment mode can be freely combined with the otherembodiment modes or embodiments in this specification.

Embodiment Mode 10

In this embodiment mode, description is made of another structure of alight-emitting element in the invention.

Although the light-emitting elements described in the aforementionedembodiment modes are mainly organic electroluminescence (EL: ElectroLuminescence) elements, the invention is not limited to these.

For example, it may be a DMD (Digital Micromirror Device), a PDP (PlasmaDisplay Panel), an FED (Field Emission Display), an SED(Surface-conduction Electron-emitter Display) which is one of the FEDs,an electrophoretic display device (electronic paper), or a piezoelectricceramic display.

Among the aforementioned light-emitting elements, elements whose colorscan be recognized with light traveling therethrough can perform adisplay through color filters as described in Embodiment Mode 3. Theemission spectrums of the light-emitting elements R1 and R2 in the firstand second pixels are varied from each other; the emission spectrums ofthe light-emitting elements G1 and G2 in the third and fourth pixels arevaried from each other; and the emission spectrums of the light-emittingelements B1 and B2 in the fifth and sixth pixels are varied from eachother. As a result, when represented by a CM-XY chromaticity diagram,coordinates on the chromaticity diagram may be varied between thelight-emitting elements R1 and R2 in the first and second pixels;between the light-emitting elements G1 and G2 in the third and fourthpixels; and between the light-emitting elements B1 and B2 in the fifthand sixth pixels, respectively.

Among the aforementioned light-emitting elements, elements of aself-luminous type can perform display by converting colors with afluorescent material and the like. The emission spectrums of thelight-emitting elements R1 and R2 in the first and second pixels arevaried from each other; the emission spectrums of the light-emittingelements G1 and G2 in the third and fourth pixels are varied from eachother; and the emission spectrums of the light-emitting elements B1 andB2 in the fifth and sixth pixels are be varied from each other. As aresult, when represented by a CIE-XY chromaticity diagram, coordinateson the chromaticity diagram may be varied between the light-emittingelements R1 and R2 in the first and second pixels; between thelight-emitting elements G1 and G2 in the third and fourth pixels; andbetween the light-emitting elements B1 and B2 in the fifth and sixthpixels, respectively.

Note that this embodiment mode can be freely combined with the otherembodiment modes or embodiments in this specification.

Embodiment 1

The display device of the invention can be applied to various electronicdevices. Specifically, it can be applied to a display portion of anelectronic device. Such electronic devices include a video camera, adigital camera, a goggle display, a navigation system, an audioreproducing device (e.g., a car audio, an audio component set, or thelike), a computer, a game machine, a portable information terminal(e.g., a mobile computer, a mobile phone, a portable game machine, anelectronic book, or the like), an image reproducing device provided witha recording medium (specifically, a device for reproducing a recordingmedium such as a digital versatile disc (DVD) and having a display fordisplaying the reproduced image), and the like.

FIG. 38A shows a display which includes a housing 38101, a supportingbase 38102, a display portion 38103, and the like. A display devicehaving the pixel configuration of the invention can be used for thedisplay portion 38103. Note that the display includes all of informationdisplay devices such as those for personal computers, televisionbroadcast reception, and advertisement display. The display which usesthe display device of the invention for the display portion 38103 canexpress bright colors.

In recent years, need for a high added value of displays has beengrowing. Accordingly, to reduce the manufacturing cost and to expressbright colors are the primary subjects to be addressed.

For example, by using the pixel configuration in FIG. 2 or the like fora pixel portion of a display panel, a display panel which can expressbright colors can be provided.

In addition, by forming the pixel portion and its peripheral drivercircuits over the same substrate as shown in FIG. 30A, a display panelwith reduced manufacturing cost can be formed.

In addition, by using an amorphous semiconductor (e.g., amorphoussilicon (a-Si:H)) for a semiconductor layer of a transistor in a circuitwhich partially constitutes a pixel portion, a manufacturing process canbe simplified and further cost reduction can be achieved. In this case,the driver circuit on the periphery of the pixel portion may be formedin an IC chip so that it is mounted on the display panel by COG or thelike as shown in FIG. 31B and FIG. 32B. In this manner, using anamorphous semiconductor makes it easier to increase the size of adisplay.

FIG. 38B shows a camera which includes a main body 38201, a displayportion 38202, an image receiving portion 38203, operating keys 38204,an external connecting port 38205, a shutter 38206, and the like.

In recent years, competitive manufacturing of digital cameras has beenintensified in accordance with the higher performance. Therefore, tosuppress the cost of a high-performance product is the primary subjectto be addressed. A digital camera which uses the display device of theinvention for the display portion 38202 can express bright colors.

For example, by forming a signal line driver circuit which operates at ahigh speed in an IC chip while forming a scan line driver circuit whichoperates at a relatively low speed on the same substrate as a pixelportion by using transistors of single conductivity type, highperformance and cost reduction can be achieved. In addition, by using anamorphous semiconductor, for example amorphous silicon for asemiconductor layer of a transistor used for the scan line drivercircuit which is formed over the same substrate as the pixel portion,further cost reduction can be achieved.

FIG. 38C shows a computer which includes a main body 38301, a housing38302, a display portion 38303, a keyboard 38304, an external connectingport 38305, a pointing device 38306, and the like. A computer which usesthe display device of the invention for the display portion 38303 canexpress bright colors.

FIG. 38D shows a mobile computer which includes a main body 38401, adisplay portion 38402, a switch 38403, operating keys 38404, an infraredport 38405, and the like. A mobile computer which uses the displaydevice of the invention for the display portion 38402 can express brightcolors.

FIG. 38E shows a portable image reproducing device provided with arecording medium (specifically, a DVD player), which includes a mainbody 38501, a housing 38502, a display portion A38503, a display portionB38504, a recording medium (e.g., DVD) reading portion 38505, operatingkeys 38506, a speaker portion 38507, and the like. The display portionA38503 can mainly display image data, while the display portion B38504can mainly display textual data. An image reproducing device which usesthe display device of the invention for the display portions A38503 andB38504 can express bright colors.

FIG. 38F shows a goggle display which includes a main body 38601, adisplay portion 38602, an earphone 38603, a temple 38604, and the like.A goggle display which uses the display device of the invention for thedisplay portion 38602 can express bright colors.

FIG. 38G shows a portable game machine which includes a housing 38701, adisplay portion 38702, speaker portions 38703, operating keys 38704, arecording medium insert portion 38705, and the like. A portable gamemachine which uses the display device of the invention for the displayportion 38702 can express bright colors.

FIG. 38H shows a digital camera having a television receiving function,which includes a main body 38801, a display portion 38802, operatingkeys 38803, a speaker 38804, a shutter 38805, an image receiving portion38806, an antenna 38807, and the like. A digital camera having atelevision receiving function which uses the display device of theinvention for the display portion 38802 can express bright colors.

Such a multi-functional digital camera having a television receivingfunction is more frequently used for television reception and the likenowadays, and longer operating hours per charge is required.

For example, low power consumption can be achieved by forming aperipheral driver circuit in an IC chip using a CMOS and the like asshown in FIG. 31B or FIG. 32A.

In this manner, the invention can be applied to various electronicdevices.

Note that this embodiment can be freely combined with the otherembodiment modes or embodiments in this specification.

Embodiment 2

In this embodiment, description is made of an exemplary structure of amobile phone which has a display portion formed by using a displaydevice with the pixel configuration of the invention, with reference toFIG. 37.

A display panel 3701 is incorporated into a housing 3730 in a freelyattachable/detachable manner. The shape and size of the housing 3730 canbe changed as appropriate in accordance with the size of the displaypanel 3710. The housing 3730 to which the display panel 3710 is fixed isfit into a printed wiring board 3731 so as to be assembled as a module.

The display panel 3701 is connected to the printed wiring board 3731through an FPC 3713. A speaker 3732, a microphone 3733, atransmission/reception circuit 3734, and a signal processing circuit3735 including a CPU, a controller, and the like are formed on theprinted wiring board 3731. Such a module is combined with an input means3736 and a battery 3737, and then incorporated into housings 3739. Apixel portion of the display panel 3701 is disposed so that it can beseen from an open window formed in the housing 3739.

The display panel 3701 may be constructed such that a part of peripheraldriver circuits (e.g., a driver circuit having a low operating frequencyamong a plurality of driver circuits) is formed over the same substrateas a pixel portion by using TFTs, while another part of the peripheraldriver circuits (a driver circuit having a high operating frequencyamong the plurality of driver circuits) is formed in an IC chip. Then,the IC chip may be mounted on the display panel 3701 by COG (Chip OnGlass). Alternatively, the IC chip may be connected to a glass substrateby TAB (Tape Automated Bonding) or a printed wiring board. By employingsuch a structure, power consumption of a display device can be reducedand operating hours per charge of a mobile phone can be lengthened.Further, cost reduction of the mobile phone can be achieved.

In addition, the display device shown in the aforementioned embodimentcan be applied to the pixel portion as appropriate.

For example, in order to further reduce power consumption, a structureas shown in FIG. 31B or FIG. 32A may be used, where a pixel portion isformed over a substrate with TFTs, and all of the peripheral drivercircuits are formed in IC chips to be mounted on the display panel byCOG (Chip On Glass) or the like.

Note that the structure shown in this embodiment is only an exemplarymobile phone, and therefore, the display device of the invention can beapplied to not only the mobile phone with the aforementioned structurebut also mobile phones with various structures. In addition, by usingthe display device of the invention, bright colors can be expressed.

Embodiment 3

In this embodiment, description is made of an exemplary structure of anelectronic device which has a display portion formed by using a displaydevice with the pixel configuration of the invention, specifically atelevision receiver having an EL module.

FIG. 33 shows an EL module combining a display panel 3301 and a circuitboard 3311. The display panel 3301 includes a pixel portion 3302, a scanline driver circuit 3303, and a signal line driver circuit 3304. Acontrol circuit 3312, a signal dividing circuit 3313, and the like areformed over the circuit board 3311, for example. The display panel 3301and the circuit board 3311 are connected with a connecting wire 3314.The connecting wire 3314 can be an FPC or the like.

The display panel 3301 may be constructed such that a part of peripheraldriver circuits (e.g., a driver circuit having a low operating frequencyamong a plurality of driver circuits) is formed over the same substrateas a pixel portion by using TFTs, while another part of the peripheraldriver circuits (a driver circuit having a high operating frequencyamong the plurality of driver circuits) is formed in an IC chip, so thatthe IC chip is mounted on the display panel 3301 by COG (Chip On Glass)or the like. Alternatively, the IC chip may be mounted on the displaypanel 3301 by TAB (Tape Automated Bonding) or a printed wiring board.Note that FIG. 30A shows an exemplary structure where a part of theperipheral driver circuits is formed over the same substrate as thepixel portion, while another part of the peripheral driver circuits isformed in an IC chip, so that the IC chip is mounted on the substrate byCOG or the like.

In addition, the display device shown in the aforementioned embodimentmodes can be employed as appropriate.

For example, in order to reduce power consumption, a pixel portion maybe formed over a glass substrate with TFTs, while all of the peripheraldriver circuits may be formed in IC chips to be mounted on the displaypanel by COG (Chip On Glass) or the like.

With such an EL module, an EL television receiver can be completed. FIG.34 is a block diagram showing the main configuration of an EL televisionreceiver. A tuner 3401 receives video signals and audio signals. Thevideo signals are processed by a video signal amplifier circuit 3402, avideo signal processing circuit 3403 which converts a signal output fromthe video signal amplifier circuit 3402 into a color signalcorresponding to each color of red, green, and blue, and a controlcircuit 3412 for converting the video signal to be input into a drivercircuit. The control circuit 3412 outputs signals to each of a scan linedriver circuit 3410 and a signal line driver circuit 3404. In the caseof performing digital drive, a signal dividing circuit 3413 may beprovided between the control circuit 3412 and the signal line drivercircuit 3404, so that an input digital signal can be divided into msignals before being output to a display panel 3411.

Among the signals received at the tuner 3401, audio signals aretransmitted to an audio signal amplifier circuit 3405, and an outputthereof is supplied to a speaker 3407 through an audio signal processingcircuit 3406. A control circuit 3408 receives control data on areceiving station (reception frequency) or sound volume from an inputportion 3409 and transmits signals to the tuner 3401 as well as theaudio signal processing circuit 3406.

FIG. 35A shows a television receiver incorporating an EL module of adifferent mode from FIG. 34. In FIG. 35A, a display screen 3502 isformed from an EL module. A housing 3501 is provided with a speaker3503, operating switches 3504, and the like as appropriate.

FIG. 35B shows a television receiver having a wireless and portabledisplay. A housing 3512 incorporates a battery and a signal receiver,and the battery drives a display portion 3513 and a speaker portion3517. The battery can be repeatedly charged with a battery charger 3510.In addition, the battery charger 3510 can transmit/receive videosignals, and the video signals from the battery charger 3510 can bedelivered to the signal receiver in the display. The housing 3512 iscontrolled with operating keys 3516. The device shown in FIG. 35B canalso transmit signals from the housing 3512 to the battery charger 3510by operating the operating key 3516; therefore, it can also be called avideo/audio two-way communication device. Further, the device can alsocontrol communication with another electronic device by operating theoperating keys 3516 such that signals are transmitted from the housing3512 to the battery charger 3510, and another electronic device receivesthe signals that the battery charger 3510 can transmit. Therefore, thedevice can also be called a general-purpose remote control device. Theinvention can be applied to the display portion 3513.

FIG. 36A shows a module combining a display panel 3601 and a printedwiring board 3602. The display panel 3601 has a pixel portion 3603 wherea plurality of pixels are provided, a first scan line driver circuit3604, a second scan line driver circuit 3605, and a signal line drivercircuit 3606 for supplying a video signal to a selected pixel.

The printed wiring board 3602 is provided with a controller 3607, acentral processing unit (CPU) 3608, a memory 3609, a power supplycircuit 3610, an audio processing circuit 3611, a transmission/receptioncircuit 3612, and the like. The printed wiring board 3602 and thedisplay panel 3601 are connected through a flexible printed wiring board(FPC) 3613. The printed wiring board 3613 may be provided with a storagecapacitor, a buffer circuit, and the like in order to prevent noiseinterruption on the power supply voltage or signals and also preventdull signal rising. In addition, the controller 3607, the audioprocessing circuit 3611, the memory 3609, the CPU 3608, the power supplycircuit 3610, and the like can be mounted on the display panel 3601 byCOG (Chip On Glass). By using COG a scale of the printed wiring board3602 can be reduced.

Various control signals are input/output through an I/F portion 3614(interface) provided on the printed wiring board 3602. In addition, anantenna port 3615 for transmitting/receiving signals to/from an antennais provided on the printed wiring board 3602.

FIG. 36B is a block diagram of the module shown in FIG. 36A. This moduleincludes a VRAM 3616, a DRAM 3617, a flash memory 3618, and the like asthe memory 3609. The VRAM 3616 stores image data to be displayed on thepanel; the DRAM 3617 stores image data or audio data, and the flashmemory 3618 stores various programs.

The power supply circuit 3610 supplies power to operate the displaypanel 3601, the controller 3607, the CPU 3608, the audio processingcircuit 3611, the memory 3609, and the transmission/reception circuit3612. Depending on the specification of the panel, the power supplycircuit 3610 may be provided with a current source.

The CPU 3608 includes a control signal generation circuit 3620, adecoder 3621, a register 3622, an arithmetic circuit 3623, a RAM 3624,an interface 3619 for the CPU 3608, and the like. Various signals inputto the CPU 3608 through the interface 3619 are once stored in theregister 3622 before being input to the arithmetic circuit 3623, thedecoder 3621, and the like. The arithmetic circuit 3623 performsoperation based on the signals input, and specifies an address forsending various instructions. On the other hand, signals input to thedecoder 3621 are decoded, and then input to the control signalgeneration circuit 3620. The control signal generation circuit 3620generates signals containing various instructions based on the signalsinput, and transmits the signals to an address specified by thearithmetic circuit 3623, specifically to the memory 3609, thetransmission/reception circuit 3612, the audio processing circuit 3611,the controller 3607, and the like.

The memory 3609, the transmission/reception circuit 3612, the audioprocessing circuit 3611, and the controller 3607 operate in accordancewith the respective instructions received. The operation is brieflydescribed below.

Signals input from an input means 3625 are transmitted to the CPU 3608mounted on the printed wiring board 3602 through the I/F portion 3614.The control signal generation circuit 3620 converts image data stored inthe VRAM 3616 into a predetermined format in accordance with the signalstransmitted from the input means 3625 which is a pointing device, akeyboard, or the like, and then transmits the data to the controller3607.

The controller 3607 processes signals containing image data which aretransmitted from the CPU 3608 in accordance with the specification ofthe panel, and then supplies the data to the display panel 3601. Inaddition, the controller 3607 generates Hsync signals, Vsync signals,clock signals CLK, AC voltage (AC Cont), and switching signals L/R basedon the power supply voltage input from the power supply circuit 3610 andthe various signals input from the CPU 3608, and supplies the signals tothe display panel 3601.

The transmission/reception circuit 3612 processes signals which havebeen transmitted/received as electromagnetic waves at an antenna 3628,and specifically includes high frequency circuits such as an isolator, abandpass filter, a VCO (Voltage Controlled Oscillator), an LPF (Low PassFilter), a coupler, and a balun. Among signals transmitted/receivedto/from the transmission/reception circuit 3612, signals containingaudio data are transmitted to the audio processing circuit 3611 inaccordance with the instruction from the CPU 3608.

The signals containing audio data which are transmitted in accordancewith the instruction from the CPU 3608 are demodulated into audiosignals in the audio processing circuit 3611 and then transmitted to aspeaker 3627. Audio signals transmitted from a microphone 3626 aremodulated in the audio processing circuit 3611, and then transmitted tothe transmission/reception circuit 3612 in accordance with theinstruction from the CPU 3608.

The controller 3607, the CPU 3608, the power supply circuit 3610, theaudio processing circuit 3611, and the memory 3609 can be integrated asa package of this embodiment.

Needless to say, the invention is not limited to a television receiver,and can be used for various applications such as a monitor of a personalcomputer, an information display board at the train station or airport,or a particularly large display medium such as an advertisement displayboard on the street. By using the display device of the invention,bright colors can be expressed.

Note that this embodiment can be freely combined with the otherembodiment modes or embodiments in this specification.

Embodiment 4

In this embodiment, description is made of application examples of adisplay panel which has the display device of the invention as a displayportion, with reference to the drawings. A display panel which has thedisplay device of the invention as a display portion can be incorporatedin a moving object, a building, or the like.

FIGS. 55A and 55B each show a moving object incorporating a displaydevice, as an exemplary display panel which has the display device ofthe invention as a display portion. FIG. 55A shows a display panel 9702which is attached to a glass door in a train car body 9701, as anexemplary moving object incorporating a display device. The displaypanel 9702 shown in FIG. 55A which has the display device of theinvention as a display portion can easily switch images displayed on thedisplay portion in response to external signals. Therefore, images onthe display panel can be periodically switched in accordance with thetime cycle through which passengers' ages or sex vary, thereby moreefficient advertising effect can be expected.

Note that the position for setting a display panel which has the displaydevice of the invention as a display portion is not limited to a glassdoor of a train car body as shown in FIG. 55A, and thus a display panelcan be applied to anywhere by changing the shape of the display panel.FIG. 55B shows an example thereof.

FIG. 55B shows an interior view of a train car body. In FIG. 55B,display panels 9703 attached to glass windows and a display panel 9704hung on the ceiling are shown in addition to the display panels 9702attached to the glass doors shown in FIG. 55A. The display panels 9703each having the display device of the invention as a display portion hasself-luminous display elements. Therefore, by displaying images foradvertisement in rush hours, while displaying no images in off-peakhours, outside views can be seen from the train windows. In addition,the display panel 9704 having the display device of the invention as adisplay portion can be flexibly bent by providing switching elementssuch as organic transistors over a substrate in a film form, and imagescan be displayed on the display panel 9704 by driving self-luminousdisplay elements.

Another example where a display panel having the display device of theinvention as a display portion is applied to a moving objectincorporating a display device is described with reference to FIG. 56.

FIG. 56 shows a moving object incorporating a display device, as anexemplary display panel which has the display device of the invention asa display portion. FIG. 56 shows a display panel 9901 which isincorporated in a body 9902 of a car, as an exemplary moving objectincorporating a display device. The display panel 9901 having thedisplay device of the invention as a display portion shown in FIG. 56 isincorporated in a body of a car, and displays information on theoperation of the car or information input from outside of the car on anon-demand basis. Further, it has a navigation function to a destinationof the car.

Note that the position for setting a display panel which has the displaydevice of the invention as a display portion is not limited to a frontportion of a car body as shown in FIG. 56, and thus a display panel canbe applied to anywhere such as glass windows or doors by changing theshape of the display panel.

Another example where a display panel having the display device of theinvention as a display portion is applied to a moving objectincorporating a display device is described with reference to FIGS. 57Aand 57B.

FIGS. 57A and 57B each show a moving object incorporating a displaydevice, as an exemplary display panel which has the display device ofthe invention as a display portion. FIG. 57A shows a display panel 10102which is incorporated in a part of the ceiling above the passenger'sseat inside an airplane body 10101, as an exemplary moving objectincorporating a display device. The display panel 10102 shown in FIG.57A which has the display device of the invention as a display portionis fixed on the airplane body 10101 with a hinge portion 10103, so thatpassengers can see the display panel 10102 with the help of a telescopicmotion of the hinge portion 10103. The display panel 10102 has afunction of displaying information as well as a function of anadvertisement or amusement means with the operation of passengers. Inaddition, by storing the display panel 10102 in the airplane body 10101by folding the hinge portion 10103 as shown in FIG. 57B, safety duringthe airplane's takeoff and landing can be secured. Note that by lightingdisplay elements of the display panel in an emergency, the display panelcan be also utilized as a guide light.

Note that the position for setting a display panel which has the displaydevice of the invention as a display portion is not limited to theceiling of the airplane body 10101, and thus a display panel can beapplied to anywhere such as seats or doors by changing the shape of thedisplay panel. For example, the display panel may be set on the backsideof a seat so that a passenger on the rear seat can operate and view thedisplay panel.

Although this embodiment has illustrated a train car body, a car body,and an airplane body as exemplary moving objects, the invention is notlimited to these, and can be applied to motorbikes, four-wheeledvehicles (including cars, buses, and the like), trains (includingmonorails, railroads, and the like), ships and vessels, and the like. Byemploying a display panel having the display device of the invention,downsizing and power saving of a display panel can be achieved, as wellas a moving object having a display medium with an excellent operationcan be provided. In addition, since images displayed on a plurality ofdisplay panels incorporated in a moving object can be switched all atonce, in particular, the invention is quite advantageous to be appliedto advertising media for unspecified number of customers, or informationdisplay boards in an emergency.

An example where a display panel having the display device of theinvention as a display portion is applied to a structure is describedwith reference to FIG. 58.

FIG. 58 illustrates an example where a flexible display panel capable ofdisplaying images is realized by providing switching elements such asorganic transistors over a substrate in a film form, and drivingself-luminous display elements, as an exemplary display panel having thedisplay device of the invention as a display portion. In FIG. 58, adisplay panel is provided on a curved surface of an outside columnarobject such as a telephone pole as a structure, and specifically, shownhere is a structure where display panels. 9802 are attached to telephonepoles 9801 which are columnar objects.

The display panels 9802 shown in FIG. 58 are positioned at about a halfheight of the telephone poles, so as to be higher than the eye level ofhumans. When the display panels are viewed from a moving object 9803,images on the display panels 9802 can be recognized. By displaying thesame images on the display panels 9802 provided on the telephone polesstanding together in large numbers, such as outside telephone poles,viewers can recognize the displayed information or advertisement. Thedisplay panels 9802 provided on the telephone poles 9801 in FIG. 58 caneasily display the same images by using external signals; therefore,quite effective information display and advertising effects can beexpected. In addition, since self-luminous display elements are providedas display elements in the display panel of the invention, it can beeffectively used as a highly visible display medium even at night.

Another example where a display panel having the display device of theinvention as a display portion is applied to a structure is describedwith reference to FIG. 59, which differs from FIG. 58.

FIG. 59 shows another application example of a display panel which hasthe display device of the invention as a display portion. In FIG. 59, anexample of a display panel 10001 which is incorporated in the sidewallof a prefabricated bath unit 10002 is shown. The display panel 10001shown in FIG. 59 which has the display device of the invention as adisplay portion is incorporated in the prefabricated bath unit 10002, sothat a bather can view the display panel 10001. The display panel 10001has a function of displaying information as well as a function of anadvertisement or amusement means with the operation of a bather.

The position for setting a display panel which has the display device ofthe invention as a display portion is not limited to the sidewall of theprefabricated bath unit 10002 shown in FIG. 59, and thus a display panelcan be applied to anywhere by changing the shape of the display panel,such that it can be incorporated in a part of a mirror or a bathtub.

FIG. 60 shows an example where a television set having a large displayportion is provided in a building. FIG. 60 includes a housing 8010, adisplay portion 8011, a remote controlling device 8012 which is anoperating portion, a speaker portion 8013, and the like. A display panelhaving the display device of the invention as a display portion isapplied to the manufacturing of the display portion 8011. The televisionset in FIG. 60 is incorporated in a building as a wall-hangingtelevision set, and can be set without requiring a large space.

Although this embodiment has illustrated a telephone pole, aprefabricated bath unit, an inner side of a building, and the like asexemplary structures, this embodiment is not limited to these, and canbe applied to any structures which can incorporate a display device. Byusing the display device of the invention for a display panel, astructure having a display medium which can express bright colors can beprovided.

Note that this embodiment can be freely combined with the otherembodiment modes or embodiments in this specification.

The present application is based on Japanese Priority application No.2005-288373 filed on Sep. 30, 2005 with the Japanese Patent Office, theentire contents of which are hereby incorporated by reference.

What is claimed is:
 1. (canceled)
 2. A display device comprising: aplurality of pixels arranged in a matrix with a plurality of rows andcolumns, the plurality of pixels comprising: a first pixel comprising alight-emitting element, the light-emitting element having a chromaticitywhose x-coordinate in a CIE-XY chromaticity diagram is 0.50 or more; asecond pixel and a third pixel each comprising a light-emitting element,the light-emitting element having a chromaticity whose y-coordinate inthe CIE-XY chromaticity diagram is 0.55 or more; and a fourth pixel anda fifth pixel each comprising a light-emitting element, thelight-emitting element having a chromaticity whose x-coordinate andy-coordinate in the CIE-XY chromaticity diagram are 0.20 or less and0.25 or less, respectively, wherein the first pixel and the fourth pixelare arranged in a first direction, wherein the first pixel and the fifthpixel are arranged in a second direction, wherein the second pixel andthe third pixel are arranged in the first direction, and wherein thefirst direction is vertical to the second direction.
 3. The displaydevice according to claim 2, wherein the light-emitting elementsprovided in the fourth pixel and the fifth pixel have differentthickness from each other.
 4. The display device according to claim 2,wherein the fourth pixel and the fifth pixel have different emissionspectrums.
 5. The display device according to claim 2, wherein thefourth pixel and the fifth pixel emit light with colors of differentcoordinates in the CIE-XY chromaticity diagram.
 6. The display deviceaccording to claim 2, wherein the fourth pixel and the fifth pixel havelight-emitting regions with different area dimensions from each other.7. The display device according to claim 2, wherein the light-emittingelement is an electroluminescence element.
 8. The display deviceaccording to claim 2 further comprising a substrate, wherein theplurality of pixels are over the substrate, and wherein the substrate isa flexible substrate.
 9. The display device according to claim 2,wherein the display device is used in an electronic device selected fromthe group consisting of a video camera, a digital camera, a goggledisplay, a navigation system, an audio reproducing device, a computer, agame machine, a mobile computer, a mobile phone, a portable gamemachine, an electronic book, and an image reproducing device.
 10. Adisplay module comprising the display device according to claim 2,comprising at least one of an FPC and a housing.
 11. An electronicdevice comprising the display module according to claim 10, comprisingat least one of a display portion, a battery, an antenna, a speaker andan operating key.
 12. The display device according to claim 2, whereineach of the first to fifth pixels includes a transistor comprising anoxide semiconductor.
 13. A display device comprising: a first pixelcomprising a light-emitting element, the light-emitting element having achromaticity whose x-coordinate and y-coordinate in a CIE-XYchromaticity diagram are 0.6 or more and 0.35 or less, respectively; asecond pixel and a third pixel each comprising a light-emitting element,the light-emitting element having a chromaticity whose x-coordinate andy-coordinate in the CIE-XY chromaticity diagram are 0.3 or less and 0.6or more, respectively; and a fourth pixel and a fifth pixel eachcomprising a light-emitting element, the light-emitting element having achromaticity whose x-coordinate and y-coordinate in the CIE-XYchromaticity diagram are 0.15 or less and 0.2 or less, respectively,wherein the first pixel and the fourth pixel are arranged in a firstdirection, wherein the first pixel and the fifth pixel are arranged in asecond direction, wherein the second pixel and the third pixel arearranged in the first direction, and wherein the first direction isvertical to the second direction.
 14. The display device according toclaim 13, wherein the light-emitting elements provided in the fourthpixel and the fifth pixel have different thickness from each other. 15.The display device according to claim 13, wherein the fourth pixel andthe fifth pixel have different emission spectrums.
 16. The displaydevice according to claim 13, wherein the fourth pixel and the fifthpixel emit light with colors of different coordinates in the CIE-XYchromaticity diagram.
 17. The display device according to claim 13,wherein the fourth pixel and the fifth pixel have light-emitting regionswith different area dimensions from each other.
 18. The display deviceaccording to claim 13, wherein the light-emitting element is anelectroluminescence element.
 19. The display device according to claim13 further comprising a substrate, wherein the first to fifth pixels areover the substrate, and wherein the substrate is a flexible substrate.20. The display device according to claim 13, wherein the display deviceis used in an electronic device selected from the group consisting of avideo camera, a digital camera, a goggle display, a navigation system,an audio reproducing device, a computer, a game machine, a mobilecomputer, a mobile phone, a portable game machine, an electronic book,and an image reproducing device.
 21. A display module comprising thedisplay device according to claim 13, comprising at least one of an FPCand a housing.
 22. An electronic device comprising the display moduleaccording to claim 21, comprising at least one of a display portion, abattery, an antenna, a speaker and an operating key.
 23. The displaydevice according to claim 13, wherein each of the first to fifth pixelsincludes a transistor comprising an oxide semiconductor.